I get obsessed with random topics and consume everything I can read about it.
When manic, I eat the exact same thing every single day - it changes from time to time, but it always something from a chain restaurant/cafe that has multiple locations. I will go to different locations each day - sometimes different locations within the same day to eat it twice.
At home, all night, I sit with a notepad and write mind-map style diagrams of stuff that I think I am realizing about a variety of topics. For hours.
I pace around my house and talk to myself and make myself laugh. Everything can seem funny. Sometimes I just sit there and laugh for no reason.
Once, I drove across the country and back twice in a 3 week timeframe - using credit cards. I have stood up from my desk and left more than one job in the middle of the way with no warning or notice.
I toss aside meaningful relationships, and I get in car accidents. I once bought over $5,000 worth of anime merch and figures in 1 week.
That is a sample of what I do when I am manic.