"Due to the cost of a bikes, I could only justify purchasing 1 bike.  I went with a race bike as well (BMC).  I am commuting to work, so I need to bring a lunch and work clothes.  I went with a rvelate designs viscacha which fits everything once I fold and roll the clothes..  It is a seat mounted bag, and I can swap it off in no time.  It also doesnt have to clamp onto anything, so it is tool free and wont scratch anything.  The only problem I have is that it sways a lot when chugging out of the saddle.  "