Third generation Girl Scout leader here. Like my fellow Girl Scouts (and Guides), I tend to bring a lot into the parks. I have a huge Lowepro backpack for my camera (DSLR), an extra lens, filters, cleaning kit, remote, extra battery, extra SD card, tripod, etc. The bottom half is padded and designed to carry camera stuff, but the top half is more like a normal backpack. In it, I carry sunscreen; hand sanitizer; sunglasses and hat if I'm not wearing them; cell phone; lanyard and pins if I'm not wearing them; lots of snacks, both sugary and low-sugar or sugar free as DBF is diabetic; mini first aid kit; ponchos for water rides; my keys, complete with a wind-up flashlight keychain; chapstick; hand lotion; eye drops (my contacts bother me a lot, but it's nice to not have to take off my glasses every other ride); water bottle; and pony tail holders. DBF and I switch off carrying it. Oh and in my pocket I carry my little wallet with AP, FPs, credit card, a little cash and ID.
DBF is a Boy Scout volunteer (and made Eagle Scout, himself). Since he's also trained in the Be Prepared mindset, if I don't take all that in, he will. This upcoming trip though, I'm trying to take just a little camera case and a smaller backpack with built in water bottle. Slowly trying to cut down. Wish me luck!