I went with a Seagull Seasonal Bag and used it quite extensively. I think for short trips to the market, it's a great thing to have and is less of a hassle than panniers. I wouldn't use it for long distance rides as it'll leave your back extremely sweaty and becomes quite uncomfortable (depending on the weight). The Seagull is a fantastic bag and I prefer it to many of the more commercial brands like Timbuk2 and Chrome. Not to mention, their customer service is phenomenal.