I bring my clothes in the day before I ride, along with an extra lunch. I keep an extra bra at work, along with a towel and hygeine supplies. I tried riding with a regular backpack; it really messed up my back. I found that if I took the bladder out of my Camelbak, that gave me some extra room and since it fits well, without stress in the wrong places, I use that to carry make up, wallet, phone, Clif Bars, leg and arm warmers, and papers to grade. It's still cool in the morning, so sometimes I have to have a totally different riding outfit from AM to PM. I keep one short sleeved jersey at work, just in case what I have is wrong.