I would go and do a food shop at your local supermarket en route to the caravan (get a cool box for chilled stuff).
Plan your meals before you set off and decide how many meals you will have out in cafes or evening meals too. We often take picnic type food with us so if we're out for the day we can have a picnic, cuts down on costs.
Then you will have a better idea of how much money you'll need. Meals are really the expensive things. Then petrol and getting in to visitor attractions if you're going to do that. Ice creams, treats, coffees etc.
Just booked my first ever holiday thats just me and the kids. 5 days in Wales in a caravan in August.
Holiday will be paid for by middle of June, and then I shall start putting up spending money, but how much will I need do you think ??
Gas and electric, and entertainment passes are included, but we are self catering, so will need food. There isn't masses to do in the area, except for a zoo, so most things will be done on site, or beach I hope. They have a good indoor pool too, so hopefully we will get a lot of use out of that.