When you get a credit card do it with enough time to spare, they can take a while to come through.
You should ring the company and let them know you are going abroad, where & when. Sometimes they say they don't need to know but do it anyway, then they won't think it's being misused & put a stop on it. Take your debit card too just in case.
It is always a good idea to purchase some small holiday items &/or something at the airport so they can follow the transactions and see that you are travelling.
Check out Nationwide, they used to have a low rate for travelling abroad. A difference of 1% compered to anything up to 3%. If you are not spending much then it won't matter so much.
Never use it for getting cash unless you are absoloutly desperate as the charges are high.
Plus a small amount of US$ for tipping and snacks at the airport as was said. Bear in mind some flights are delayed so this is a really good idea as SL said.
P.s. I've just checked and they (NW) are currently quoting 2% so do a search and see if you can get better.