I've done super-cheap family vacations before when I've been able to drive and I have a microwave where I'm going.
We fill one cooler full of just food for once we're there. We plan one full meal (either lunch or dinner) back at the hotel. Some fav's.....hot dogs (microwaved in a dish w/water), tacos (I cooked up the taco meat and froze it before we left), sloppy joes, my "cheater" spanish rice (lipton spanish rice, chicken or hamburger meat, mexi corn and cheese melted on top), soup and sandwiches, chicken fettucini (Lipton fettucini mix, some broccoli, and diced chix.---I actually bring a can of chicken, it's easier, but you could do it cheaper with regular chicken)......well, you get the idea. For shorter trips, where I didn't have to pack as much, I've brought casseroles and goulosh all prepared. I also love brining our portable gas hibachi and bbq in the parking lot. When we've gone somewhere for a longer period of time, I've also brought my griddle (usually fits great under the back seat of the van, where you can't fit a whole lot else) and sometimes the crock pot. Pancakes are really cheap and filling and the kids love them. I get the Hormel pre-cooked bacon at Sam's club and I can microwave that in moments.
We always pack a separate cooler for the trip. When we bring the grill (and the weather is okay) we stop at parks along the way and let the kids get out and run and eat a nice filling lunch.
As far as tips in the park.....not a whole lot you can do....I agree about bringing in snacks. I saw this posted on the Budget board a long time ago, but it rang true. The poster indicated that she brought a big plastic bin that was filled with snack items (fruit snacks, raisins, granola bars, candy, chips, dried fruit, etc, etc.) and each child had either a fanny pack or a back pack that they carried into the park. Each morning, the kids were told to each get at least two items from their packs. That kept away the "I'm hungry" and "I wants".
Also, I've always found that when kids think of money as "theirs" vs. "mom and dad's" they are much more careful in spending it! So, if you have $80 that they can spend ($10 for each of them), hand them the $10 at the beginning of the trip and tell them they can spend it on anything they want (that you would allow them to have, of course) and that's it. Let them know what you will be covering and that you expect them to cover the rest. If, for example, you will cover one snack and the meals, let them know that anything else, whether food, souvie, or experience comes out of their money.
Make homemade autograph books before you go. Get some big pens (they work better with all the gloved characters) from a local dollar store (I've also seen them in the dollar bins at Target, too.) Print out a bunch of Disney color pages. Buy glo sticks/necklaces from somewhere cheap, and that way when the vendors come around, you won't have to worry about them being left out or anything.
While in the park, collect everything that has any Disney branding...make a game of it with the kids and with the plan to make a family vacation scrap book when you get home. There are tons of things! All the hand outs, maps, schedules, etc. Also, that would maybe stear them towards "finding" good post cards to add to the scrap book, instead of the more expensive finds at the gift shop. Take the time to take a ton of pictures! It also helps focus you back on the "experience" and trying to remember everything.
My thoughts and prayers go out to you and your family for your sacrifices! I'm so happy for you that you get this experience before your DH leave!