The single most iconic image of Halloween is the Jack-o-lantern. The tradition of carving pumpkins for Halloween goes back many generations and carving pumpkins at your party is a terrific activity to help get your guess in the Halloween spirit.
Break your guests up into teams of 2-5 members and make sure you have a pumpkin for each team. You can provide pumpkin carving tools for everyone or encourage some of your guests to bring their own. Gutting the pumpkins makes a mess so be sure to have trash bags at the ready. Once the teams are done put a candle or pumpkin light in each and take pictures of the teams with their creation for a fun keepsake. You can make it a contest where the winners are awarded a prize or just call it a fun activity where everyone wins.