I also use the FairFX. Although I do take credit cards as well and use the Post Office fee free mastercard for most of our expenses. Been using FairFX since 2010 and very happy with it. I use it for some online purchases in US$ between trips as well which is quite convenient.
Just remember not to use it as a hold card for a rental car or hotel as it is not a credit card and they will put a hold on your funds, meaning depending how much you have loaded onto the card, you might not have access to your cash for a while.
Thomas Cook and some others also do a travel money card, as does the Post Office. The rates are slightly lower than FairFX but they work just the same. However, beware of inactivity fees if you aren't going to be using it for a while between trips. ALways read the fine print because it may be to your advantage to close it when you return and just get a new one for the next trip if you aren't going to the USA within a year
EDIT: Sorry OP, just seen your ticker and realized you don't really have time to apply for a FairFX