Ok, here's what dh, dd4 and I pack for a day in the parks:
sunglasses (1 pair each)
sunscreen (smallest bottle we can find)
bandaids or moleskin (just a few- not the whole box)
sunhat (for dd)
digital camera (with extra battery and memory card, in waterproof protective case)
tylenol (itty bitty bottle)
trial size purell (although I never have used it- same bottle for 3 years)
2 bottles of water (we share- family germs don't count)
dh carries room keys and credit cards in his wallet
Family vacation experience has taught us that we'd rather have to do without stuff than lug extra junk around with us. (I had an epiphany in Washington DC when I unpacked an overstuffed backpack and a diaper bag for the 5th time in one day at museum security

) This way we can use a sling type messenger bag and keep our hands free, and we don't really miss most of the stuff.