This is a great first day/week activity for getting to know students, and they will love it because it involves candy! They randomly choose an M out of the bag, depending on the color they choose they will answer a question about themselves.
Trick-or-Treat Scavenger Hunt - FREE PRINTABLE - Keep the fun going even after the kiddos are finished trick-or-treating this year. Not only is it fun, it's a great way for parents to do a safety check of all of the kids' treats at the end of the night.
Balloon Rockets - I've done this in several science camps I've conducted. Kids have fun with it. But, when the balloon deflates it may fall off the straw because it's surface area changes - another good thing to show and explain to kids.
Paper plates, Popsicle sticks, and a balloon are all you need to play Balloon Ping-Pong. (Not sure how sturdy the paper plates would be, but may be able to do something similar for a carnival/game night social event theme.