If you're in a theater where you can see the audience from the booth, it's fun to keep an eye on more engaged audience members and their reactions.
Another fun thing to do is discuss the play itself on headset during longer periods without any cues. When I ASMed The Threepenny Opera, we used to have in-depth conversations about why Macheath did this or Jenny did that. If you're able to watch the show and chat at the same time, it's a great way to keep alert.
So you're not taking line notes or watching blocking for maintenance?
Whatever work for you...but I can't say I could condone in-depth chatting on headsets in any circumstance.
(Besides, I think when you reach 100+ performances, you are generally dealing with understudies/swings being put in as actors take vacation time, call in sick, etc., on a regular basis.)