I know some of these have been mentioned but here are some things we have purchased ahead of time either at the
Disney Store on sale or online with Disney (on sale also) -- so I won't have to spend TOO much on souvenirs while there! Kids loved them and did not care one bit that they weren't bought while there. LOL
Disney mini-fans (on sale $2.99)
pins to trade (on sale like $1.15 each awhile back- traded for other pins while there instead of paying $6+ for pins to trade!)
Disney T-shirts (all matching! Except on the mickey/minnie ones... us girls had red Minnie shirts and caps, my son had mickey blue shirt and cap) $5 each
Flashlights- the castle type on the end for the girls, buzz lightyear round end on the one for my son -can't remember how much but it was cheap... and I'm sure it was quite a savings over what they'd cost at Disney World!
Those twirly light things- whatever they are called. LOL I bought each of them one (different ofcourse) and they loved them.
Princess lightup/music wand
Swimsuits, coverups, swimshoes, and beach towels... and blanket backpacks. All on sale/cheap.
Oh and stuffed animals... I would much rather get those on sale at the disney store than at the high costs at Disney World! I never get away with not buying ANY while at Disney World... but I lessen the cost to the pocketbook by bringing along many of the ones we got cheaper. I've bought some on ebay in the past also.
If you are unable to find a good price on things before you go- be sure to check out the "everything under $10" store at DTD. I don't know how long that's been there but we just discovered it our last (recent) trip. Ofcourse everything in there is under $10 and I was amazed at how much lower the price of some things there were that were the exact same things we'd just seen at World of Disney for much higher! Also they (at that time- YMMV?) had a section of wall that anything there was 4 for $10. We got lots of goodies there- including yet another Minnie for my youngest. So technically that cost us $2.50 but we saw the exact same Minnie at World of Disney for $13. I like that kind of savings. Ditto for the princess lip gloss (pkg of 4). $2.50 there (in the 4 for $10 deal on the wall) but it was $8.50 at World of Disney. And her light up princess necklace- $2.50 instead of $11 at the other store. (the last item out of 4 I couldn't decide.. nothing the other 2 wanted out of that section of wall and they had things like Alladin but not Jasmine-- and my son isn't into stuffed dolls. LOL And they had Ursulla there... on that section of wall- but not Jasmine. So I chose a Disney World DVD. LOL)
So even AT Disney you can get a good deal if you know where to look- so that's why I'm telling you about this... so you can shop there if you like, before spending way more at World of Disney!
Good luck finding great deals before you go! I can't tell you how much I have saved on souvenirs buying them at a discount before going. Some of those things they used on the last trip in 2003- and used them again this last recent trip. I'd rather pack them than pay a fortune for everything (x 3 children that I have) while there.
Oh and I had purchased Disney pens, Disney backpacks (the smaller kind for flight there and back/if they wanted to take extra things with them to the parks, etc.), and a variety of other Disney stuff to take with us to amuse and delight my kiddos- on ebay awhile back. So that's an avenue to look into- but I don't really do ebay anymore because of being burned a few times awhile back. So just be really careful if you use ebay.