I found a powerful idea at Rena Klingenberg’s Jewelry Display Ideas blog: Ever had a booth that was too far from electricity when you exhibited at craft fairs? Bring your own power, for lights & credit-card processing!
How to BYO? Virginia Vivier’s article there has two great suggestions, with solid details given:

Portable battery
- Battery power
- Rechargeable 12-volt battery setup — powers the whole booth!
- Laptop credit-card processing — use freely downloaded software
- Cellphone credit-card processing — get a wireless merchant account

Flexible solar clip light
- Solar power
- Rechargeable clip lights — LED technology makes these efficient and long-lasting
- Solar cellphone charger — self-explanatory
Images here are from Vivier’s excellent article!
Thank you so much for the mention of Virginia Vivier’s excellent article!
I’ll make sure Virginia sees your post here too.
Hi there, Rena! Thanks for popping by — and for passing along the word to Virginia!