I've been using this Trek bag:
for the last two years, and I love it. The trunk portion is the perfect size to hold my lunch & clothes, and I can get my laptop in the fold-down panniers when I have to transport it. Unfortunately I've completely killed the zipper on the trunk portion. I'd replace it, but it's expensive as heck for what it is--around $80. Plus my LBS has done a terrible job of getting one in.
I've seen many other trunk/pannier combos that are cheaper, but I haven't found any others where the pannier pockets are wide enough to fit a laptop. The few that do have them are usually at least as expensive if not more.
Does anyone have a recommendation? Or....is it possible for a non-handy person to replace the zipper with good results?
Oh, before anyone says "messenger bag" or "backpack", I hate riding with stuff on my back if I can avoid it.