Roy - For some reason I missed that bike riding was already being discussed - hmmm. Pay more attention.
I don't really know too many compact ways to get the cardio up. Cycling, stair climbing etc. And even though the energy produced is small, may as well capture it.
I remember seeing a tv article a long time ago where a family had thier kids create energy for watching tv by stationary cycling. It seemed real at the time.
Bike shops have bins full of old bike tubes that are free for the taking, and make great weight training machines that you can fit in a backpack.
Boxing is another great workout,that can be far more useful than three step aerobics if you get in trouble with an ******* in a back alley.
When you are cold, a few minutes of shadow boxing gives you a quick warmup, with added benefits.
Brent
Somewhere back in the dawn of time there was a stair stepper advertised that was just the steps and would fold down so it fit under a couch. You had to anchor it so that it wouldn't tip and hold on to an upright of some sort. I haven't seen one for many years so it may be the kind of thing you have to find at a garage sale but it does have the advantage of being small. Depending on the cofiguration of your cockpit you might be able to exercise while at the wheel.
sk