This one is a little strange, although I have stranger ones I won't mention out of embarrassment....
When I'm feeling hypomanic, I'll take the main characters from books I've read and start to write a sequel (or prequel) involving those characters. Or I'll come up with stories of my own and brainstorm names for each character by writing them down for a few hours straight. I always found it to be an outlet for my mania/hypomania that doesn't get me into any trouble.