Chris, at least the battery-power option is easy: buy a Cellularline charger (like the model PB-03S). It has 4400mAh and can deliver up to 2A… really enough to drive the pi and at least a 3.5 TFT.
See http://computarium.lcd.lu/works/
for a picture of my assembly including a very sexy Rii miniature wireless keyboard with touchpanel (and Laser pointer on top!)
