Leave. Go for a walk, or a coffee, or go home. Nobody knows you aren’t in a meeting room.
If your co-workers are into it, have a LAN party. I used to work at a place that had a daily management-approved kill session. It was good.
I take a 30 to 40 minute walk (2 miles) every day at work. Sometimes it’s to clear my head. Sometimes it’s to think about work. Sometimes it’s to think about not work. No one cares, and if they did, I’d argue it’s time well spent for the company. I can’t get anything done if my brain is overflowing with crap.
Man, a work LAN party would be pretty cool.