caffeine is very good. taking time away from it makes it work well on climbs. I find it brings a positive attitude to climbs and a general "psyched to be there" feeling. but maybe that's just the addiction talking.
my cell phone has the game "Snake" on it that has consumed many hours of my time. my gps does not have this feature. therefore I vote for cell phone. seriously, "Snake" is a big part of my life