There are a ton of great "Battery Banks" on the market that give you the ability to carry several days of charge.

Beyond that, Solar (150w) in a fold up pack that can be mounted to a backpack that charges a "Battery Bank" while on the go would probably be my next choice.

I have also seen some "Fuel Cell" options out there, that look good, still have the limitation that once you run out of "cells", your stuck. The energy density is better than batteries, but your still capacity limited.

A lot of brands have already been mentioned here, but I have fondness for Anker. They are price competitive, and have a wide array of Banks/Panels and Chargers for every need.

I personally own several of their products, and have never been disappointed.

Rod