WE've done the food in the room thing and discovered this: it doesn't really save all that much, and sometimes ends up costing more!
At WDW, time =money. If you are driving to WDW, then it makes more sense to stop at a store on your way. If however, you are flying in, it makes less sense - ESPECIALLY - if you check in to the resort before hitting the grocery store. Also, if you are thinking you'll go back tothe room to get lunch, you will be locked into doing just that. Again, you lose too much time.
Generally, we find it's just better to share quick serve meals.
My two exceptions are bottled water, coffee in the room - and maybe - at some point in the trip - bringing back a few muffins or something. Maybe a dessert - if you'll have afridge. If not, then maybe a bag of chips or some little snack. In order to have coffee in the room, we'll pick up a bottle of milk - perhaps inthe resort gift shop. Sometimes we'll stow leftovers if we're headed to the room right after dinner. Often, we even end up tossing those.
In the last three years, we have bothered even less with having meals inthe room. The dining plan is more than enough food for us. Also, so many of foods that are in the 'prepared and won't spoil' category are highly processed stuff that is just SO unhealthy. Like Pop Tarts, yuck! I also remember when my mom used to make us drink canned orange juice in the 70's. That stuff was SO nasty! Even healthy sounding granoloa bars are often loaded with corn sweeteners.
Three food itmes that can be tricky to find on property: certain drinks (like: Pepsi products, diet ginger ale, any juice beyond apple or orange), fresh fruit, and any yogurt beyond Yoplait (I think that's the brand DIsney buys). So if you have certain foods that you can't live without, or a medical condition - then you might want groceries. Disney fruit is usually limited to the cheap stuff: apples, Sunkist oranges, melon, bananas. Real FLorida oranges are available just off property! (on 192 is a great stand that looks like a giant orange!) (Dont' buy the ones they sell at the airport!) (Indian River is just a short drive from Orlando, and a neat day trip!)
DO try a DIS search - since the advent of DDP these threads have become more rare...but once auopn a time - there were LOTS of great huge threads about all the foods you could prepare in your room. (using just the coffee maker for hot water or perhaps the food court's microwave)
If you are going to buy some premade meals at the grocery store - I suggest Publix - esp the one at the intersection of 192 and 535 (Kissimmee corner of WDW). they have a big sections of really nice looking prepared meals. At least the last time I was there.
I suggest avoiding
Walmart, unless you plan ot eat a LOT of food or can REALLY limit your family to all eating the smae thing. Walmar tends to stock LARGE boxes of items. You won't save money if you end up throwing away half of what you buy (or bringing it home?) be really careful to buy ONLY what you know you will eat.
One last tip - if you don't plan on grocery shopping...stores now DO have shelf stable milk. Parmalat is one brand. It won't save money over just buying the bigger cartons on property, but milk is the only perishable item on your list, then it is worth doing.
We DO still drink bottled water. Dasani is just FL water ina bottle, so you if that's your water brand, you might as well just buy a few bottles and refill them from the tap.