If you want to be really hardcore, do what I saw a friend of mine doing once:
- Pro Nikon camera
- Backpack with multiple motorcycle batteries connected to transformer
- Laptop also in backpack plugged in to transformer
- 1394 (mini-Firewire 400) cable from camera to laptop
- Two HDDs in laptop with RAID 1
Works great for pictures and video alike.
Backpack was a bit heavy though at nearly 20kg. Also a small risk of fire, electrocution and/or battery acid leakage.