Our general rule is $175 per day, per person. There are days we stay way under that, and maybe only a few days we go over (which all evens out). This figure includes food (groceries & dining out, mostly mid-range places), booze & cocktails, beach expenses, gas, pretty much everything besides airfare, room & rental car. I'm sure everyone's budget is very different but this works for us to make a pretty good estimate of what we tend to spend.