I consider myself to be on the frugal side, but no way this would work for our family. I do have 2 CM DDs, so that really helps, but when we go, we want to spend as much time as we can enjoying the things we love the most in all the parks. I do laundry and don't mind cooking (when we do my scrapbook shows, we often are having soup in our room in the evenings). I grew up travelling Europe in a 15' trailer with our family of 5, so I think that plays into my idea of "vacation" somewhat w/ my own DDs.
that said, Earl of Sandwich is also a less expensive place to eat...the sandwiches are HUGE ($5.75 ea), so we get 2 meals out of them (well, Mr-Ultra-Metabolism doesn't, but he's in a grocery line item all his own...

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As far as free souvenirs go, at Epcot, there is the plastics display inside the Innovations building. Kids get to "build" a computer robot and race it (lots of fun), then afterward, get to put together a plastic one to take home for free. There are also the masks at the World Showcase and now they've added KidCot stations in Future World, too, which allows for a little sit down and a little creativity. There is also Club Cool where you can stop in for a refreshing Cultures of the World lesson with free soda samples.

You can make your own autograph books and collect autographs, making a scrapbook later with your own photos; it's fun to try to get hard-to-find characters. Take lots of photos, not just of the family, but of the details, the architecture, etc.
Another can-be-inexpensive souvenir is trading pins. I buy them from eBay from a seller that runs about $2/pin (sort of a grab bag), then DDs can trade them for the ones they really like. They recently got quite a few "hidden Mickey" pins and some CM exlusives by trading.
In DTD, there is a store that sells grab bags (I thought they were around $7?) that usually has all kind of fun stuff. My 11yo penny pincher LOVES these and takes great joy in adding up the retail cost of what was in the bag.
ETA: we also buy something called Real Lemon (in the baking aisle) and carry the packets with us to add to water bottles, plus a few packets of sweetener/sugar/stevia powder and you have lemonade. Most of the time, we drink water, but sometimes, we just need a little pick-me-up!