Something fun to do to pass time at a semi- formal birthday party?

If you’ve seen my other question, I’m still planning out my 16th birthday party. What I want to do, is have a semi formal birthday party. Not tooo formal, but dresss up and stuff.
Some music in the background, decorations around the room..Food on the tables, they get it themselves, Pita’s, fruit platters, punch bowl…
For activities, so far I might want to do a Chubby buddy contest (stuff as many jumbo marshmellows in ur mouth as u can and the one who can stuff the most wins a prize).
What else could i add in for the activities to keep my guests occupied? I don’t want a dance at my party, it’s just too hard to get them to start dancing, and maybe just something fun to do indoors. (It might be somewhat cold outside during this time around my city)
And for those wondering, I’ll most likely just rent out a big room at some place downtown.. soo, anymore suggestions? (PS: sorry if that was hard to understand or read.. haha)