Sort your mail out – to a parents house is better than a PO box, or at least to someone you trust to open and read mail to you. (do set up a redirect from your addy to the one you trust to catch “odd” stuff.
Bills – get reading off the gas/leccy etc.
Leave about a grand in the bank account if you can, you’ll be surprised how often you’ll want/need UK cash.
make sure any loans etc are paid off, do not rely on money being moved internationally on time. Don’t care what they say, don’t rely on it.
Cancel all Credit cards, but keep a current account open.
also – move all the stuff linked to your current work email to a internet based one. Things like paypal have to be closed down, trust me on this close your paypal account if you move countries otherwise you can get stuck with a limited paypal account good for nothing if it’s hijacked at any point.