Checklist suggestions:

Toys to share maybe: but if you bring things to share, they must be quiet toys.

For the water park:

swim suits
flip-flops
goggles and such

For gamers:

head sets /headphones
power cords
computers
game systems
memory cards
(I don't know what you'll need, but whatever it is, bring it.)

Power strips and extension cords might be needed, or not. If people with plenty of room and a spare power strip could put them in the car just in case, that would be great. Mark them, maybe.

Board gamers:

I'm bringing:

Chronology
Writey-Drawey
Wise and Otherwise
Five Crowns

If people have other board games that can be played by a large and variable number of people, that would be good.

One request: Please Do Not bring "Cards Against Humanity," or if you do, keep it in your room. Too disturbing for mixed-age, mixed-group.

Everybody:

Extra set of car keys, if you're driving
Electronics and paraphernalia
Camera, extra batteries, chargers
Phone, charger
Computer (if you do that sort of thing when travelling), cords, chargers

Food for the rooms (we can't have it in the conference center, but stock your car and room, maybe).