With apologies to campers and hikers who know all about the Hiking 10 Essentials. Same idea, different situation. This list is intended to make your trip to the Parks better, and is the result of my many, many trips to Disneyland Resort (both pre- and post-"resort.").
1. Sunscreen. You’ll need it. Many people don't realize how much water and light-colored concrete is at Disneyland Resort, all radiating the sun’s rays at you from every angle while you walk around and stand in lines. People visit Southern California because of our great weather: we can have 70F days, even in winter... and with those warm days, you'll need sunscreen.
2. Comfortable Shoes. Do you remember being 16 and being able to walk all day in flip-flops? Yeah, me too. As the years go by... well, you know how your own feet feel after a day of walking. At Disneyland Resort, you will be walking...and standing---a lot! (I usually walk 5-8 miles in a day at the parks.).
Wear comfortable shoes for walking on concrete. Different people swear by different shoes, but the critical elements are arch support, cushioning and thick soles. Thin-soled shoes won’t cushion your feet against all of the parks’ cement walkways.
3. Hat. A ball cap, visor, or hat with a brim to shade your face. Hats are sold everywhere in the Parks, for $19-$20+…your choice to buy one there or bring your favorite. Any hat (or visor) with a bill or a brim is better than no hat. I really like this Nike featherlight visor (click on "visor" to the left) because I can squish it inside my backpack without it getting ruined. It's made of Dri-Fit, so it dries quickly too.
4. Moisture-Wicking Socks. Wear your favorite performance hiking socks (aka synthetic, or light wool) that wick moisture away from your skin. (No cotton) I like Thorlo socks because they have a thick cushy sole that doesn't feel bulky. Like these for women, and these for men.
5. Sunglasses (and case and/or Croakie). You'll be alternating between outside and inside for most rides (“attractions” is the proper Disney term), so what will you do with your sunglasses when both hands are holding a ride “bar?” I use a Croakie like these on mine, and keep my regular glasses handy for evening and "inside" rides (safely inside the case, in an outside pocket of my daypack). If you aren't from California, be aware that Anaheim (like most of Southern California) can be sunny and warm (or just sunny) any day of the year.
6. Small wallet or lanyard. You'll want to have your park entrance ticket (or Annual Pass) in a convenient place to grab FastPasses during the day (and your FastPasses will go in this also). I never again want to be that person that everyone else is waiting for because I can't remember where I stashed my park ticket, Annual Pass, or FastPass in my backpack...or maybe it's in a pocket of my shorts, or my jacket. (Yep, I've been that person.)
Many people use a lanyard (above, worn hanging from your neck) with an attached plastic pouch for this purpose, and Disneyland sells lots of different styles of these. (Since I'm short, the pouch hangs low and gets caught on things… like ride seat belts. I've had more than one pouch rip and I've had to ask a Cast Member to retrieve it (with my annual pass) from whatever ride I just finished. I've recently found this cute Mickey Mouse pouch with lanyard from Amazon.com (it comes in other Disney characters, too) that is perfect for a Park ticket or Annual Pass, FastPasses AND my iPhone (at least up to a 5S size) fits inside! It's been with me for many trips to the parks and it seems like it will last awhile.
I've also used a small wallet like this one (also from Amazon.com) that fits in my shorts or jacket pocket.
7. Waist Pack or Daypack. A waist pack (aka fanny pack) makes carrying your stuff (ID, money, credit cards) easier, is relatively secure against pickpockets if you wear it in front, and keeps your hands free. Yes, people do wear fanny packs at Disneyland.
I usually bring a small backpack/daypack because I seem to carry a lot of STUFF when I'm in the parks. (The REI stores don't carry the one I have now, but you can find it here--on sale, too. See this page for lots of similar daypacks.) If it’s small and squishy enough, you can usually cram it in beside you on rides that don’t provide storage space for personal items. Mine has lots of pockets and compartments, including outer pockets for my water bottle and sunglasses.
8. Snacks. Snacks at Disneyland and California Adventure are more expensive than in the real world (What? $2.79 for a 20 oz bottle of water? $4 for the $1 Costco churro?). Officially, Disney asks that no outside food or drink be brought into the theme parks.
Unofficially, the “no outside food” policy isn't stringently enforced. Bags, purses, backpacks and such are searched by Disney security at the the entrance, but a few items in your daypack (like a piece of fruit, crackers, carrots, energy bars, sealed/unopened plastic bottles of water and hiker-type water bottles) are ignored. I use plastic “Tupperware-type” containers for my snacks (instead of baggies) and never have a problem. But, just like at the airport, don't bring a bunch of sandwich makings (like peanut butter, even in a plastic jar.)
You absolutely will NOT be allowed to bring in hard-sided coolers, large coolers, glass containers, alcoholic beverages, (or selfie sticks).
If you eat your snacks discreetly, without using park resources (e.g. don't sit at a restaurant table without buying anything), and you don’t make a mess, no one will say anything to you.
9. Water bottle. At many of the park restaurants, you can fill your water bottle at self-serve soda machines while you are eating a meal, and, if you're nice about it, your server at a sit-down restaurant (Disney calls these “table service” restaurants) will refill your water bottle, too. I like this Camelbak insulated bottle because it has a "bite valve," which prevents accidental spills of water all over me (and anyone sitting next to me) since you have to bite down on the valve (clever, aren't they?) to make water come out of it. The insulation really does keep my water cool on even hot days.
Drinking fountains are near every restroom and scattered about the parks. (DLR allows hydration packs, but I've never brought one. Why carry the extra weight if getting refills is so easy?)
10. (in winter) Poncho (and extra socks). It's fairly well-known that most southern Californians freak out when it rains. At Disneyland, this means that they (and most visitors from out of the area) LEAVE the parks when it starts raining, or postpone their trip if rain is in the forecast. Soooo…. if you are prepared for a little rain (which usually doesn't last long), the lines for the rides will be shorter (YAY!). If rain is in the forecast, buy a poncho and put it in your backpack just in case. Southern California grocery and variety stores (think Target) put out their portable racks with ponchos and umbrellas anytime it rains. These are definitely cheaper than in the parks, but the Disney Park ponchos do have Mickey and other characters printed on them. Wear a baseball-type hat (or visor, under the poncho hood) to keep rain off your face. (Extra socks in case your feet get wet—duh!) Don’t bring an umbrella; they're a hassle to carry and drip everywhere, like on other people in lines.
By the way, we get most of our rain in winter. But even then, it's not very often.
10. (dry season) Flip flops. In summer (and other warm weather), bring a pair of flip flops (or other sandals or shoes that can get wet). You'll want them for wearing on wet rides while your walking shoes stay dry inside your pack (at Disneyland) or in the free lockers (near Grizzly River Rapids at California Adventure). DLR only has two water rides that will get you very wet; though you could get wet watching the World of Color water show (at DCA). If it's a REALLY hot day, I've seen people walk near the edge of the Bugs Land sprinklers (at California Adventure) just to catch some spray to cool off (really, they are for kids... but aren't we just big kids?).
DON'T BRING: a selfie stick. Disney is serious about this one and will confiscate selfie sticks that guests try to bring into the parks. You've been warned!