Definitely eat in the room. My cousin packs a box of cereal and the spoons and disposeable bowls. This leaves room for items you might buy. We eat cereal bars, bagels and fruit. This also saves time in getting to the parks in the morning.
We use the Brita bottles, too. You can save a ton of money and calories by drinking water from these rather than buying lemonade or soda. They are also good for good tasting water in the rooms.
Pack snacks like peanut butter crackers or fruit snacks.
The best money saving idea is to set the amount of souvenier money you will spend. Get Disney Tshirts before you go. They are much cheaper that way.