To what extent do those who hold to a 'literal' account of Genesis 1-11, such as YECs, hold there are symbolic elements in Genesis 1-3?

There is some dispute over what "literalism" refers to (see Wikipedia); I'm of the opinion that it should not be of used of genre-aware interpretative approaches, but others apparently say that the common historical-grammatical method should also be called "literalism", even though it recognises non-literal genres such as poetry as well as smaller textual features like idiom and metaphor. But either way, it doesn't matter too much to this specific question...

Young Earth Creationists do not teach that Genesis is to be understood strictly literally, but instead that it should be read as a historical text. Lita Sanders in the Journal Of Creation describes Genesis as "ancient historical narrative":

I identify Genesis 1–11 (indeed, the book of Genesis as a whole), as ancient historical narrative—each word in this term is important. This doesn’t dispute that there are poetic elements with the typical parallelism that characterizes Hebrew poetry. However, they always involve someone speaking, e.g. the climaxes in Genesis 1:27 (by God), 2:23 (by Adam), and 4:23–24 (by Lamech). These just reinforce the contrast between the quoted poetry of the speakers and the main narrative text.

‘Ancient’ reminds us that we cannot impose modern historiographical notions on an ancient text. Just because we write history in a certain way does not mean that we can impose those rules on an author writing thousands of years ago. Instead, we must ask, “If an ancient person wanted to write history, how would that look? What grammatical constructions would he employ? What details would he include in the document?”

‘Historical’ anchors our thoughts on the fact that Moses intended to communicate about actual people, places, and events in history. When he presents Adam and Eve as the first people God created and the parents of all mankind, he is not giving us a metaphor or an ‘everyman’ parable about why people sin; he is telling us about our actual first parents, back to whom every person can trace his or her genealogy. When he writes about Noah gathering all kinds of animals onto a huge ark to survive a global Flood he is not relating some sort of ancient memory about a really big flood in Mesopotamia; he is telling us about the actual event that inspired the many flood legends in ancient cultures around the world.

‘Narrative’ indicates that Moses is telling us these historical events in a story form. This is not the only genre that can encode historical information; in fact, many of the psalms speak in a poetic form about what God actually did for Israel in history. But narrative is the most straightforward genre for historical information, and relates facts in a story form without much symbolic language.

Historical texts can have figurative features; indeed idioms are so common we often don't even notice that we're not using words with their original "literal" meanings. Genesis 1 isn't in the genre of poetry, but it could be called constrained writing, because the number of 7s in the chapter is too high to be a coincidence. Two examples from these early chapters of Genesis that creationists think may not be fully literal include:

• the "firmament" of Genesis 1:6-8
• the "windows of heaven" in Genesis 7:11, 8:2

So while individual elements can be taken literally (a "day" referring to one day-night cycle, what we'd now call a 24 hour day), others aren't. Since that's the case I don't think it really makes much sense to call the whole approach "literalist", as I think it implies taking everything literally, but just note that others disagree and may call people literalists even though they frequently reject literal readings.

So on to the elements you asked about:

1. The angel and sword: I haven't found much at all that addresses whether or not Creationists take this literally or not. (To be fair, it's among the least theologically interesting or relevant parts of this fascinating and dense chapter!) One commentary on Genesis 3 by Jonathan Sarfati calls it a manifestation of the Shekhinah Glory. Which kind of throws the question on its head: if God is performing some sort of manifestation in front of Adam and Eve, then just like other manifestations (Moses and the burning bush, God appearing outside Elijah's cave in 1 Kings 19, etc) it is indisputably symbolic, but also very much real at the same time. And like the appearances of angels, I think it's an open question whether a spiritual being is manifested by the production of some kind of physical body (which is implied in instances like Genesis 18 when angels eat food), or whether photos of light are generated but without a source object, or whether the image is created directly in the mind of the observer.

2. Tree of Life: I don't think the text is really interested in how exactly eternal life and the Tree of Life are related. Likewise the question of whether death is something that would naturally occur before sin but is held off by God, or whether God introduced death once sin existed, is not one that can be clearly answered by Genesis 3. So Lita Sanders points out that there is a diversity of views within creationists over whether the Tree of Life was symbolic or truly active. I like what Peter Gadsby says, linking it to another symbolic food:

   The Tree of Life stood in the centre of the Garden of Eden which elsewhere is called ‘The Garden of the LORD’ (Genesis 2:16–17). It was a real tree, to be sure, but let me suggest that it was also symbolic of the fact that God was, and is, the source of eternal life and blessing. Adam and Eve were to have their life centred in Him, even as the Tree was in the centre of His Garden.

   Other parts of the Bible also mention The Tree of Life. In Ezekiel 47:12 we read of trees whose ‘fruit will be for food and their leaves for healing’. This image is taken up also in Revelation 22:2. It is clear particularly in Proverbs where a number of things are referred to as ‘a tree of life’ (wisdom (3:15), the fruit of the righteous (11:30), desire fulfilled (13:12), and a soothing tongue (15:4)) that the Tree of Life in these references symbolises that which brings joy and healing to people.

   This, I suspect, was what the original, the real Tree of Life in the Garden of Eden symbolised. It was material, yet it stood for the blessing of eternal life which God would give to Adam and Eve, and their descendants, if they were to pass the test of obedience. They were permitted to eat of any tree in the Garden except the Tree of the Knowledge of Good and Evil on pain of death (Genesis 13:10, compare Isaiah 51:3 and Ezekiel 28:13).

   Now, use a little lateral thinking. What else in the Bible is real and material, yet at the same time symbolises the life which is in Christ and points us repeatedly to Him? Something in which Christians share, and which reminds them that Jesus’ death brings us life? It is the sacrament of the Lord’s Supper.

   Now, let us return to the Garden of Eden. I want to suggest that the Tree of Life was there to perform such a sacramental function. If Adam passed the test of obedience, it would be the means of God’s imparting eternal life to him, not by magic, but by the working of his Spirit ‘by, with and under’ the fruit of the Tree.

   I'd point that many other Christians see the Garden of Eden as a proto-temple, though Gadsby doesn't make that point, and I'd suggest there's a symbolic through line of sacramental foods from the Tree of Life, the Israelite sacrifices (most of which were eaten by the priests and those bringing the offering, rather than entirely burned away), and finally communion.

3. The serpent: Though Genesis 3 doesn't make the identification, creationists do generally see the serpent as a manifestation of Satan. If that's the case, then like I said above, it's an open question on how the spirits manifest themselves to humans. Was there really a physical talking serpent, or just a vision in the eyes/minds of Adam and Eve? Who could say for sure! Russell M. Griggs uses the example of the Legion that enter the herd of pigs to conclude that Satan used the body of an existing serpent. Robert Gurney says that is one possibility, but that like the angels in Genesis 18 it's also possible that Satan could appear in a new physical form.

I hope these examples show that for creationists it's not so simple to say whether or not something in the text is literal or symbolic. That's because a large amount of the Bible is concerned with symbols made real, literal physical objects and actions with symbolic meanings. And because, particularly with the early chapters of Genesis, we're potentially dealing with spiritual manifestations, which have no definitive explanation.

But ultimately, to creationists it's not really important whether or not these events have physical existences or not; what matters is the historicity of these foundational chapters of humanity. What matters is that we understand that God created a very good and unblemished world, that the heads of humanity, Adam and Eve, wilfully sinned, that this separated humanity from God and brought death and suffering into the world, and finally that God gave the hope of salvation and reconciliation. The most important thing in these chapters for creationists is the historicity of The Fall, as all non-historical understandings are seen as having grave theological consequences, with serious consequences for how passages like Romans 5 and 1 Corinthians 15 are understood. Individual creationists may have opinions on whether, for example, the sword was an actual physical object or just some kind of vision, but they wouldn't be dogmatic about those views.