That $75 for a 1Gig stick is a steal. Get it now.
While reading files/music/movies off of the stick is less power consuming than reading it from the UMD drive, that power savings will be countered by the screen always being on. You can adjust the brightness of the screen to get you a bit more time, but there's no way to turn off the screen entirely without shutting down the system.
Just look for a power outlet wherever you go, and you should get by.