I went to Disney at the beggining of June and I am really grateful about some tips I got on this board and others regarding thinks one should pack when going to Disney.
1- It rained cats and dogs while we were there. This was actually great because we did not have to step on long lines for any attraction. Actually, we walked right in on must of them. This was priceless specially with our small child who gets very irritated if having to stand online for a long time. I packed the RAINCOATS for everyone and a mini umbrella. And we really used it. I wish I have packed a mini umbrella for everyone because everyone wanted to use the only one we had PLUS the raincoats. In this line too...I am glad i brought a small towel with me to the parks every day, because it allowed me to dry the stroller every time we got out of an attraction so our child could ride it confortably. I wish I had brought a big trash bag to cover it (like they recommended me here!) while we were inside the attraction. Next time I will.
2- I brought a fanny pack and a backpack. It was extremely useful. But it was a bit overpacked. I am planning to make it lighter next time. I had a lot of regular size products on it, next time i will carry them only travel size items (like sun block, etc)
3- I am very allergic and I am glad I had my benadryl there because i Need it, specially when we went to outdoor attractions with hight humidity and vegetation. I wish i had brought an antiallergen matress cover. People that are allergic to dust mites sould consider this because dust mites can live on matress even if they are very clean. This can affect your sleep if you are allergic like me.
4- I am glad i brough 2 disposable cameras instead of a regular one because it was easy to carry, no batteries need it, etc. I also gave one of the cameras to my kid and told him it was his to take pictures of whatever suits him. This allowed me to take pictures of him and everyone else without him wanting to "see" through the camera (he is young and curious) or asking me to use my camera to take a picture of something like "someone's feet!!haha
But next time I think i will bring one more camera or consider buying one disposable for everyone in the group.
5- I am glad we did not brough a stroller because it was so convenient to rent it in the parks and the kids really love the "car" concept. My 5 year old thought he was too big to be on a stroller but did not mind it at all when the cast member told him that this was not a stroller but a CAR
I hope my post helped you.