Upvote:3
You can enter visa-free for up to 6 months, but the challenge on arrival at the UK border may be demonstrating that you are a genuine visitor, having presumably spent the past year building a life / working in the UK. The standard advice is that you should bring the same documents you’d need to apply for a visa, to show to officers at the UK border. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/549692/Visitor_Supporting_Documents_Guide_-_English_version.pdf Having an onward ticket would be advisable (or at the very least, proof you have funds to buy one), and it would be even better if you could show a compelling reason to leave IMHO.
Not having any of the documents listed on gov.uk may not be a problem, or you may get a lengthy landing interview but be admitted. Worst case you’d be denied entry.