Hi, happy planning!
Ok, so something I didn't see listed yet, you can mail yourself a package to the resort if you want to bring snacks/supplies but don't have room in your luggage... it all comes down to how much you can fit in your luggage and which airline you're with (meaning how much they charge for luggage fees). You might mail bulky/light things like boxes of cereal, but pack heavier things like juice boxes in your suitcase (weight allowing and packed inside some sort of container to keep them from bursting...) There are threads on how to mail the packages if you search the site, but basically I think you address it to the resort and label it "Hold for Guest (your name here) Dates of stay (your dates here) and then you pick it up at check-in, but do your research, since others have done this and I haven't.
Things I have seen people talk about here, but haven't tried yet are 1-crystal light to put in your free cups of ice water 2-bobbles (sort of like a water bottle with it's own filter inside. Apparently the Florida water flavor doesn't sit well with some people.
I found a soft-sided cooler at our local grocery store (Giant) that has a pretty black and white pattern and looks a lot like a purse. Disney only allows soft-sided coolers for bringing things into the park, and I am planning to use that back for bottled water and fruit (we are planning to buy most of our meals)...bonus, I bought it last spring when we started planning, so I've already gotten a year of use out of it.
I'm also planning to have large ziplock bags to double-wrap our leftovers before they go in the cooler. My girls never want to eat at mealtime, but the minute the table is cleared, they are "starving", so we save the food and give it back to them later... plus our last day we plan to have a "picnic of leftovers" at AK, with a fallback plan of buying something there if there aren't enough leftovers or we're feeling picky or whatever

For that meal I found a soft-sided cooler/picnic set for $10 at Kohl's the day after Christmas, so we can be all "civilized"

(And while I truly hope to re-use it in the future, if it gets messy, at $10 I wouldn't cry if it ended up getting ruined and pitched)