I've never shipped ahead of time but know quite a few people who have. Pretty much anything you can think of that you don't need a whole package of. Of course the list would vary if you had a car or not to go to a grocery store. I would just think of what you would normally pack in a suitcase and anything that wouldn't be wrecked or spoiled being shipped pack it up. Again this would be things you won't be bringing back with you as then you'd have return shipping costs. Diapers/wipes and other baby things are a great idea. One tip I always give people is to pick up a duffle (Walmart has them) that you zip into a small flat circle but when unzipped holds a whole lot! I use that for dirty clothes and things like that for flying home. I can fit a weeks worth of my clothes in there it unfolds that big. That way I can use my suitcase for all the things I bought while Disney shopping! (also a good idea if you are shipping things that you want to bring back with you...sippy cups, bottles etc)
I ship tons of stuff to the resort. We stay for over two weeks and DH already has issues with how many suitcases I bring. I pack things like the kids cosumes (they bring a ton) water/spray fans, light up spinners, collapsible cooler, and "tinkerbelle" gifts. I also pack an extra lightweight bag "suitcase" to bring the tinkerbelle gifts home in. The rest I ship back.