Make sure you've let your bank / credit card company know that you're coming out so they don't try and freeze your card. Otherwise:

1. You'll end up in an emergency and won't be able to pay for something
2. You'll have to spend ages on the phone trying to get it unlocked.

I did it just before I came out this time, as it happened to me in the US 2 years ago. I then tried to ring back to the UK but the operator said he needed my credit card to authorise the call (which I was making to get the card re-authorised). AAAAGGHH. Luckily he was a nice operator and put me through anyway, pays to be polite to people