Picked up a Goal0 solar panel and tested it out today. In the photo I have it strapped to the back of my bike, but I may also try putting it on my camelbak backpack.
In June I'll be biking across Michigan over the course of six days and camping out each night. This makes power outlets pretty scarce. I'm not planning on bringing any big electronics but I do want a working phone the whole time. I'm hoping that a whole day in the summer sun will be enough to charge the battery pack during the day which would then charge my phone at night. I'll be experimenting with it over the next few months and will post again when I have more experience with it.