It is a bit of an urban myth that Disney parks don't allow you to bring in your own food for a picnic or drink - it is untrue.
Of course, Disney would like you to feed yet more euros down the greedy mouth of their megacorporation mouth by stuffing your own mouth with their Mickey Mouse Burgers. At least other theme parks like Alton Towers allow MCDonalds, KFC and the rest of the heart-attack merchants in (and they don't ramp up the prices).
Disney just object to large picnic baskets. Fair enough, pack all the snacks and drinks you want in your baggage. Drinking fountains are also plentiful, so don't throw away your empty plastic bottles. Not sure what they are like about letting in a proper drink...ummm
dont forget to bring comfortable shoes, you`ll be doing a lot of walking here, in fact bring two pairs, the surfaces are very uneven and when it rains there are LOTS of puddles, you`ll be glad of dry shoes the next day
waterproofs are highly recommended, if you dont bring one then you`ll need to buy one of these stylish capes, which cost 7 euro and make you look like a duck
Photo Equipment: you are going to take LOTS of pictures here, dont forget film / memory cards, there are camera shops on the parks but they are expensive
Wear a pair of comfortable walking shoes. The distances you need to walk are huge. Especially when you plan to switch from one park to another. Also take out a least 20 minutes to walk back to your hotel.
Most attractions in Disney are indoor and the queues are mostly protected from the rain too. So don't let the rain spoil your journey. A casual/ sporty rain coat will do.
And if you happen to be caught in a thunderstorm... all shops sell "Mickey" rain ponchos :-)
Photo Equipment: There is a special photo shop, both in the Disneyland Park and the Studios, so if you happen to forget something... don't worry, you'll find it there.
Miscellaneous: For the ladies among you... make sure you have a handy bag, style little backpack. Don't carry too much with you, you'll need to take alll your stuff into the thrill rides!
Luggage and bags:
There are lockers at the entrance to Disneyland for you to store bags and anything you have bought throughout the day.
Clothing/Shoes/Weather Gear: You will be doing a lot of walking, so comfortable shoes are a must. The weather in this area is not always great so a waterproof may be a good idea. They do sell cheapish waterproof ponchos here.
Photo Equipment: You can buy films in many of the shops, also digital memory in selected shops.
Miscellaneous: You are officially not allowed to bring food and drinks into the park. People will look into your bag at the entrance but they won't look under your coat and they don't look in the bottom of the bag either... Psst, I told you nothing ;)