I was at PO Riverside this past Sept/Oct. Darn! I knew there were some pictures I meant to take around the resort!
Their general store "Fultons" had a section by the change rooms where they sold grocery type items. I'm sure the other Moderate resorts would have a similar selection. (I did check out stores at resorts with DVC, eg AK, BC, CR & BW, and they had additional items, as well as a frozen food section).
Here are some of the things I noticed at POR's store:
--water & skim milk in 1 & 2 litre containers (and I'm pretty sure whole milk & chocolate)
-- hard liquor (rye, gin, that kind of thing... don't drink it, so didn't pay much attention)
--bottles of beer & koolers "by the each" (beer: $5.95 each!!!!

)
--bags of bagels, loaves of sliced bread
--cereals, jams, peanut butter.
--donuts (?krispy kreme?)
--big bags of chips, tortilla chipp. Bottles of Salsa, containers of Dip.
--First Aid supplies, Pharmacy Supplies.
Fultons doesn't sell fruit or veggies, but fruitcups, fresh fruit & veggie sticks are sold and also avail as
DDP snack options at the food courts.
I didn't check out Hess, but plan to this Fall (there's one at DTD across from Parking lots & another at entrance to Boardwalk Villas/Inn parking lot entrance).
I did check out Goodings and Winn Dixie:
I walked (I like to explore walk, so 30mins walk is nothing) from DTD along Hotel Blvd, and checked out Goodings, then I walked North at that intersection up to Winn Dixie & got groceries then walked back to DTD,
The price difference was noticeable, and of course the selection was way more extensive. .... A bag of apples, 1/4 watermelon, and bunch of bananas cost about $10 at Winn Dixie... vs $1 apiece at the Food Court. And I think 6-8 Bud Lite cost me $8 there!)
AND! They don't sell Becel or Celeb in Florida... that's the number one thing I brought with me.... well, that and my Red Rose Tea!
AND! FYI, you can't buy chewing gum at WDW!