Buffy is definitely partaking in the water zone, as well as the fireworks.
Maddie will also be in the water zone, the rides and games (sorry in advance, she's competitive) and watching the fireworks. She will also take part in the hot dog eating contest!
Mal (and with the okay of Hoshi, Harry) will be there for the fireworks and dancing. She'll also show up for the cook off because free food and might just try her hand at the pie eating contest. If there is a strawberry pie, she will inhale it regardless.