The generator's weight is in the magnets and windings. To generate 5W average from 1/2 of the leg's motion, the generator must be capable of at least 10W output, and that's going to be several pounds for an off-the-shelf component. Once it's customized for the application, it might drop to under a pound.

Jumping on the dream wagon for a minute - if some of your muscle cells were cultured and attached to a small linear generator, then implanted in your body with electrodes to stimulate them, you could generate your own electricity. Might have to bring more food on the trip though!

Regarding your hiking pole generator - a variable field linear generator (kind of like those flashlights, except the magnet is replaced by an electromagnet) would allow a "damped" feeling to the pole, rather than a "springy" feeling. The only drawback would be the added weight. Hiking poles that are heavy can be tiring to use.

But the one idea that I'd develop if I had the time and money is a device that would have a part that fit in the mouth. Chewing on the device would generate electricity, and as many gum addicts will attest to, chewing takes very little thought.