Small portable solar panel to trickle charge your devices? Then you don't need to worry about power consumption.
I've looked into these, but the ones that put out adequate power are quite bulky and heavy. I can, depending on which bike I'm riding, charge a camera battery off of the engine while moving, but it's awkward and again, only possible on certain bikes.
On my bike, I installed a trickle charging device (to keep the battery charged when I store the bike for winter), and the special connector on the device works both ways, so when needed I can plug normal 12V devices on the connector. On my bike trips I bring e.g. 12V cell phone charger. If I really wanted, in theory I could bring my inverter, and thus get the standard 110V/230V AC for small power devices (~<300W).
For the solar panel, because you're space limited, you don't want the big ones, but small one combined with e.g. 10Ah power pack. The small solar panel will charge the power pack over time, and then when needed, you can power devices with that. If you want big enough panel to directly power devices, then they are big/bulky. I think e.g. Duracell has those power packs you can charge with small current USB, and it'll give large currents when needed.