Dress for the season. You'd think it would be warm all the time in southern California, but it can be cool and damp in late May. Therefore, watch the weather report and dress accordingly. Wear comfortable shoes because you're going to do some tall walking.
Toiletries and Medical Supplies: Sunscreen is in order for the summer.
Photo Equipment: 35mm camera (nothing fancy), but please buy your film at home because it costs a fortune in the park.
Luggage and bags:
If you plan to stay, then make sure you bring some fresh clothes, else stay dirty hehe
Clothing/Shoes/Weather Gear: I went there once in December and I was surprised that the weather dropped to 50F so bring along a jacket
Toiletries and Medical Supplies: Their restrooms are available at every corner and it's Free!!
Photo Equipment: Yes bring lotsa films. They post signs that say 'Photo spot' or something like that, so that's where you should be taking all the pictures hehe and of course you would be running after any characters that might appear in public hehe or you can make appointments to have a photo session with them in person.
Camping/Beach/Outdoor Gear: no camping in Disneyland!!