Unfortunately, for me, it never seems that I "pop" into a grocery store with any success. The whole process...even at home where I am familiar with the store and the brands is never less than 3 hours, by the time I park, shop, check out, load groceries into car, drive home and unload groceries.
(I have even started regularly using my local grocery store shop at home method (by internet). It costs ten dollars, but I save way more than that on time and money spent on impulse buys.)
Our first WDW trip, I did go to Publix to stock our Fort Wilderness cabin, but for me, it was an every day drudgery infringing on my vacation.
Last trip, I ordered breakfast items, snacks and booze, and someone else did the shopping while I was still en route to POR on magical express. I sat by the pool and waited for delivery.
Now, to me, that's a vacation.
This time we are renting a pool home with 14 people. I don't mind sitting at my computer, planning meals and making a grocery list before I leave...but it is worth it to me, to place an order and pay $10 a family to avoid the grocery store during my first day in town and to have that HUGE order delivered while I sit by the pool.