It depends a bit on the season. In summer, I get some stuff in advance, but mostly about 24-48hours before we leave.
If it is a transition season, I probably ash summer clothes about a week before we go.
There are also some items that are good to buy in warm months. Many places sell rain ponchos in the camping section, but they go away in winter. Now might also be a good time to find clearance sunscreen, clearance ponchos, and maybe back packs. If you like travel size toiletries, you probably want to get those a little in advance. From now until Nov2 is best time to buy costumes, if you plan to bring them.
You'll want your park tickets early enough to make FP+ picks. If you plan to do something like convert cc points to a giftcard, allow plenty of time.
I also do a fair amount of last two days prep: watering plants, pedicure, maybe mail stop, empty trash and coffeemaker, unplug a few appliances, take care of pet needs, pay bills, clear out the fridge, etc.
I never go to WDW without quality walking shoes. Those need to be broken in a bit if you need new ones. Never skimp on footwear! Big bonus for a pair of waterproof shoes!
Shopping a little for new stuff is also fun before some trips. If you have kids, and it is winter- you might NEED to buy new swim suits or summer clothes, socks, undies, shoes. One famous trip, a nephew had grown two sizes over just the fall months! Nothing fit.
If you'll have a car, there is a good outlet mall just off WDW property. But that could put a good dent in your plans if you have to spend half a day shopping.