In reply to captain paranoia:
I've considered this too, using my tablet as a GPS device when out and about. I'm not sure how practical it is though... my old nexus 7 has rubbish battery life and same for my Galaxy S3 phone.
If I use the GPS in either, the phone/tablet will most likely be dead after 3 or 4 hours, if not close to dead!
Your best bet is to probably root the device, and then stop all un-needed functions that run in the background so that it becomes a GPS-only device when you want it to.
I have a solar panel that I use sometimes, mostly only when camping or travelling to try and get some extra juice. The decent ones are expensive though. You can also get USB battery packs that take standard AA batteries
EDIT:
http://www.casehappy.co.uk/nexus-7-waterproof-cover-241-p.asp?fo_c=251&fo_k...
cheap waterproof cover, not very nice but does the job!
Post edited at 13:11