Ok, so I'm a little late and hope you had a great trip.
I hiked the JMT last summer and over a 16 day period, only fished five times. Lyell Canyon, Marie Lake, Wanda Lake(no fish), Rae Lakes, and Hitchcock Lakes. After the long days of hiking, I just didn't feel like it. However, when I did take the time, the fishing was excellent. A lightweight pole, spin-cast real, a clear bubble with a 2 lb leader, and a who knows what assortment of flies is all I really ever use.
I usually get more fishing on the shorter trips. If and when I do the JMT again, depending on funds, trying out the much lighter Tenkara set up looks good. Although you loose the casting option, the are a lot of places that the fish are up close. I guess it just depends on the person doing the fishing. As mentioned before, ((There is a "fishing" topic on Sierra Topix forum.)) Keep it simple and light, and enjoy..