If you are bike-commuting, you are already a "cool-kid". No worries there! I agree with others here that a pannier or two is the way to go. I hate having anything on my back when I'm riding, and having your extra weight lower on your ride keeps bike handling issues to a minimum. Even riding with just one pannier heavily loaded - a gallon of milk, plus other groceries - is no problem. I've used one of my Ortlieb Sport Packer Plus bags as my daily commuter bag for the past 8 years or so, and it works perfectly for me - both for commuting, and for errands/groceries. Ortliebs are also waterproof, and extremely durable - if eight years of wear-and-tear/Minnesota weather are any indication - and are super easy to load securely, and remove from a bike rack. Also, no straps to get caught on anything. Happy travels!
