Write down who holds each account, what transfers to you, and when. The list covers the CMS account, the domain, the analytics property, the design files, the code or theme, the backlog and the record of what was tested. For each item, the agreement should say whose name it's in today and what you receive on final payment or on exit.
Lean Labs' guide suggests asking an agency directly what would be yours if the engagement ended before the project did. Ask for the answer as a written term in the agreement, so both sides are working from the same wording later.
Material the agency brought with it needs its own line. If the site is built on the agency's own theme, modules or tools, ask what license you get to keep using them after the engagement ends, and whether another team may modify them.
Anything licensed from a third party needs a line as well. Fonts, stock images, plugins and software subscriptions each come with a license that someone holds, so list each one with its holder. Where a license carries a recurring charge, list who pays it. If a font or plugin is licensed through the agency's account, find out what happens to it when the engagement ends.