As spudqueen says, it depends where you are going.
I would definately take a credit card as almost everywhere takes one and it saves taking loads of cash or travellers cheques.
While things in the USA are often cheaper than here in the UK it is surprising how much money you can get through on a holiday in the USA.
If you are going to Orlando, or any area with theme parks, then entry to these parks can be VERY expensive, although it is much cheaper to buy multi park tickets for multiple days.
Once inside food and drink can be expensive so you can get through a lot of money visiting theme parks.
If you are staying in a villa then I assume you will be having breakfast in the villa which will save you money. I guess for lunch you will mostly be eating out, but maybe you can prepare some food for lunch in the morning. For dinner you can sometimes eat out, other times eat in.
And of course the petrol for a 12 seater van is going to set you back a fair bit for a 2 week holiday, but you can put that on credit card.