score:7
According to the Thai Customs authority, food is a restricted good which requires a permit to bring into Thailand and you must declare it by going through the "red lane" at customs.
However, many travelers report that it is not a problem in practice to bring small amounts of prepackaged food clearly for personal consumption. It depends on your tolerance for risk weighed against how desperately you want to have these specific seeds with you.
Note that many delicious snacks are readily and cheaply available in Thailand; you can probably find chia for sale there, but even if you have trouble with that, I'm sure you'll find something you want to eat.