national insurance number (apply once employed, allow 3 hours @ local welfare)
identification (try and get something with a local residential address on it)
internet access
PO box, mobile phone
stereo, personal computer
hints
verbalise a vision statement (so you know why you're going)
find out where you can work, and what needs to be done about visas
get a working visa (you may need to leave the country to change your status)
contact a few employment agencies before you leave (use local branches of international agencies)
fix up your resume (before you leave)
have some spare passport photos handy (for ID cards, etc)
estimate likely expenses per day
ensure your vaccinations are appropriate for the countries you plan to visit
set up your international roaming
see whether you are eligible for an international student card
If you're planning a long stay overseas, pack up all your stuff in decent boxes and stash it. Before this, sell or give away anything you no longer need.