I'm going to leave on a bus tour of Europe soon. I figure that all this time on a bus isn't going to be good for me, so I was wondering if there is any exercise I could do on the bus. For example, I've heard you can buy these things you can squeeze that will improve your grip strength (don't know what their proper name is). I'm curious if there is anything else that would work well in the confined space of a bus?
Update: I changed the title back to "What are exercises you can do on a bus?" as I think buses are a special case of space confinement and need to be treated separately.