I tried a few non-digital options as well, without success.
Graph paper + colored pencils had inconsistent colors and it was difficult to work at small resolutions.
Colored sand (sand painting) does not work well for pixel art, and it was messy as well.
Most of the cheap android tablets that have come out recently have a short battery life (3 hrs or less).
I don't think that there is a good solution for this yet.
Tourist