I could learn most of a page of not too difficult piano music.
Referee an article or two.
Read 120 pages of a novel.
Produce a not too bad drawing of something.
Watch a movie.
Walk six miles.
Shop for, cook and eat a meal.
Memorize two short poems.
Write 8 blog posts.
Write an outline of an article I want to write.
Write an abstract for a conference.
Prepare for and teach an 1:15 minute class.
Listen to music for two hours.
There are many things you can do in two hours. We have 8 hours to sleep, so that leaves 8 blocks of two hours. If you work just four hours a day during the summer, you can do two significant work-related things.