From a local that has been to BG from the time she was knee high to a grasshopper:
It's hot here, but it's not super hot. We're in a really bad dry spell and are in desperate need of some rain. Everything is crispy here. It's been about 95-100 here every day for the last couple of weeks with high (80% or greater) humidity. It's not Florida hot, but it's hot.
Refillable mugs are right at $8 and you can refill them all day long anytime you go for $1. The cups are huge. Don't think the little cups you get at the resorts in Disney. They sell straps (I don't remember how much I keep reusing my old one) for the cups. I suggest getting them. It helps keep your hands free.
You can walk through Colonial Williamsburg for free, but if you want to take a tour it's going to cost you a little bit (if I remember correctly, it's not very expensive, but it has been quite some time since I went on one). If you're driving here, the streets in downtown Williamsburg can be difficult to navigate (lots of one ways). Just try to be patient.
Personally, I don't think the meal vouchers are worth it. My sister and I tried them for giggles this summer, and we felt that we could get a way better value paying OOP. The main problem with the meal voucher is that it's only good at certain restaurants at the park, and when we went (early May) many of them were closed (it was a seasonal thing; I'm sure if we went now they'd be open) and they didn't tell us when we purchased them.
While on meals, I 100% recommend eating at the Smokehouse in the park. In my opinion, it's the best meal in the entire park. (Just thinking about it, maybe I should make an evening trip to catch the new fireworks show and have the smokehouse for dinner

). Everything at BG and WC is counter service.
Das Festhaus is probably (IMO) the worst meal on property, but everyone flocks there because it's inside in the AC
Pepsi and Hardees's usually run promotions for discounts on tickets. Unfortunately, I'm not really great at watching out for discounts as VA residents get a discount ticket, but those two usually run promotions every year.
The good thing about going to Williamsburg is not only do you have BG and WC, but you're not far from other things to do. The VA Beach ocean front is about 2 hours from there, so it's feasible to make a day beach trip if your family wanted.
I have food allergies (someone asked about eating there with them). Don't expect the same catering that you get at Disney when it comes to food allergies. The food, overall is pretty food allergy friendly. If you're very concerned because of your allergy, stop at guest services when you enter the park (it's on the right) and they can get someone from catering to answer many of your questions (I'll warn you now, it may take a while, but with allergies it's worth it).