Potentially capture the flag might be fun, it's something Sterlyn (our local Inaho) and I had considered before. Or something like a scavenger hunt; maybe people can get the items listed from participating in other activities or watching demos or such and we could just have a list of where the things come from. Though what'd work for a prize I'm not sure...

Also which parts of the school will activities be hosted in? That'd help us figure out activities we might add on.