I use a small frame bag on my roadie (on my third bag). +1 on the one-handed zipper. Also +1 on the easy access outer pocket. That is where I would like to put my hanky/nose-wiper thing. Also, if you're thinking of keeping it on the bike, perhaps a loop so the zippers can be locked with a small lock that you keep in the bag, or on one of the loops, or if you can figure out a way, have some sort of way to lock it with the same cable lock you'd use on the bike