Take snacks and breakfast food with you (poptarts, granola bars, etc) to eat in the hotel. We absolutely never eat breakfast out on non-travel days while vacationing. Of course, if your hotel includes free breakfast, make it a big one, and snag a couple of apples on the way out to snack on later.
Mom and I split meals several times last year, and we also tailored our ordering. Two hamburger meals + 2 hamburgers and split the 2 fries between the 4 of us.
Give the kids $x each and don't give in to requests for other purchases. We did that last year and it was amazing how little they bought knowing they had to use "their" money for it. My older ds actually made sure not to spend all his birthday and other monies b/c he knew he wanted a wand *and* other things. You can look online to get a good feel for the prices of souvies you might want and plan accordingly.
If you buy snacks at the parks, just do it once a day, and only for the kids. Mooch off theirs, LOL. OK, mostly we bought only for the kids, but Mom and I had to have butterbeer. It's also easy to share snacks. The boys shared a butterbeer and Mom and I shared one. And we tried to pick "iconic" things - we bought snacks at Honeydukes, Dippin' Dots at USO (we don't have one here), waffle spears at Legoland - stuff we couldn't get elsewhere.
Start saving your change RIGHT NOW. Spend no more change between now and when you leave, and use the change for mini-golf. We've done this for years to collect spending money for a day at the closest amusement park. Now we do it to help fund boy scout high adventure trips.