We have breakfast in the room, so our grocery list is heavy on breakfast foods - cereal, eggs, pancake mix, butter, bread, milk, orange juice. We get peanut butter and jelly under the thought we can make sandwiches. Microwave popcorn for my son. We eat lunch and dinner out. A case of water (which goes into the freezer) and a case of soda (we pick up a bottle of bourbon at the Screen Door).
I've heard of people pulling off Thanksgiving Dinner in their units. Myself, if I were going to cook, I'd look for the easy stuff - the spaghetti and tacos sort of meal that has been mentioned. (Someday, I know we will bring people who are less well off than we are, and we'll do a budget trip and that will involve cooking). If you are driving, a lot of people make room for a crockpot (I think some people keep them in Owner's Lockers, too), and do crockpot meals, which makes a lot of sense to me, since you throw pork in in the morning, and take pulled pork out in the afternoon.
The kitchens are fairly decent apartment like kitchens, well stocked for most uses, but I wouldn't try and go all Mario Batali in them. You'll run out of mixing bowls and pots
ETA: don't forget things like salt and pepper, any spices you need, coffee filters, coffee, sugar, etc. If you do carry on your luggage, the idea of getting shampoo and sunscreen is a good one (even if you don't, I get sunscreen, I pack some too). With the exception of laundry detergent, you'll find enough basic cleaning stuff in the unit (dish soap and dishwasher detergent), but if you want something other than some dish soap and paper towels (for instance, a lot of people want Lysol or something), bring or order that.