Everyone says "do something else with your hands." Right, sure. I have trouble finding something that works. But I may have found a pretty good one.
The health center on my campus gives out stress balls. And I've tried stress balls before and they didn't work. So hear me out you anti-stress ball peoples! :)
This is a homemade stress ball. It is made out of two balloons (make sure they're pretty strong...none of those cheepo flimsy ones). One is inside the other so it's a double layer. And fill it with sand. Don't go too full. Though I guess you can fill to your preference. Mine is filled so it's a little smaller than a fist. It's really moldable--I like that.
Anyway, it works pretty well. Just watch out that you don't get sand everywhere!