One of the most useful things I've had while traveling is a small bluetooth gps receiver. For me it is very handy as I can use it with a PC and PC mapping software such as M$ streets and trips, or if I'm traveling lighter I can use it with a portable device such as a pocket PC/smartphone/palm/etc.
I also save a lot of bulk by trying to carry all devices that charge the same way, usually by USB. Currently my smartphone/PDA, gps unit, camera, and a few other devices all charge via USB. I also found a Nimh AA/AAA charger that runs off of either 120vAC, 12vDC (car) or USB.