It seems funny to me how many include Ponchos on their list. Don't you know 'It never rains in California"? It really doesn't. It rains sunshine. I think the majority of the time we have great weather.
Is this sort of thing some continued "hazing" sort of joke? At least half, probably more, of our trips have included rain. I grew up in CA (albeit San Jose), and it rains there. It rains in So Cal too. But there's always a comment like that...it's so odd.
I bring a poncho for myself b/c of rain possibilities and for the water rides. DS and DH don't wear ponchos, and they go back to the hotel when it rains (wimps!). Their dislike of rain at DLR caused me to get my first ride on Grizzly...in December, after dark, in the rain, oh yeah....
What I have to pack? Clothes, money, two pairs of shoes, and admission. Though with APs, as long as I packed enough money, I could even forget the APs and still get in ($20 per person to get a new one printed if you lose them). Everything else is extra. Well, actually, toothpaste, b/c we don't use fluoridated toothpaste, and I don't feel like spending my vacay hunting down a Trader Joes etc to get what we use. Oh, and arnica cream and other homeopathics.
Of course, we pack a whole lot more, but those are the essentials for us. Everything else can be replaced or ignored for the trip.