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!