I just fidget with any pens I have lying around. Usually twirling them or just taking them apart and then scrambling to put them back together when a new slide comes up.
Does having a dedicated item for fidgeting help? To me I feel like it wouldn't really help because I'd forget about it and subconsciously start messing with my hair, my pens, or really anything around me. I also build things when I fidget, I was in bio in highschool and before I knew it I had a tower made of my water bottle, erasers and a journal.