Yeah man, use your imagination. Pick up a pencil and doodle, write your thoughts as they come (actually a pretty cool experiment, I've done some amazing and productive thinking through just writing what I think as I think it, tends to direct itself to problems in my life, it makes you slow down your though process and consider everything more closely, or it's gibberish and nonsense, which is fun too)
Booze it up, I've spent an afternoon with a bottle of whiskey and a good book, drank and read until I couldn't read any more (there was a point about six shots in where my imagination got really vivid and it was more like watching a movie than reading a book,) then when you can't read anymore your drunk and can go find your own fun waaay easier.
Go jump around a playground, seriously, it's fucking AWESOME! Take your shoes off and squish your toes in the mud. Rain + bare feet is win as tits. And tits are pretty damned win.
Hmmm...I dunno man, use your noggin. I'm going to be starting to carve my own set of norse runes once I find suitable bones, that'll occupy my time on trains and shit while I'm travelling this summer.