I feel your pain!  I've been on crutches for the last month with an ACL injury and have been going a bit stir-crazy.  I've been going to the pool and have been able to sit on the step and move my legs in a bicycle motion.  I can't actually ride a bike yet but when I can put more weight on it, that will be my next step.  Your suggestion of kayaking is great too - you can get outdoors and get some exercise.

I've gone fishing with my husband a few times; I can't really walk around much but I bring a chair and just it's nice to be out in the woods.  I've also spent some of my forced time indoors planning a short backpacking trip for later this year when I can hike again. 

I also found a great book about trees that has helped pass the time too (The Overstory).

Good luck on your recovery!