I wear a VB hipster (full-size, not the mini) which carries BOTH my essentials (camera and phone in a ziploc to guard against splashes on water rides, KTTW card handy in the outside zipper pocket) and the kids' essentials (wet wipes, extra undies in case of an "accident," extra sunscreen, sunglasses, and a first aid "mini kit" containing band-aids, blister pads, ointment and headache medicine). We don't carry any beverages with us: full bottles are heavy and all the counter service locations will give you ice water for free, on request.
The hipster is lightweight and effortless to wear: the crossbody design means I don't ever have to take it off, and it zips securely so I needn't worry about anything getting lost on a wild ride.