Does any one have any suggestions for a bag that would have a pocket or sleeve for a water bottle? I'd prefer an external pocket so i won't worry so much about spills. I need to carry a MacBook Air 13, binder and a water bottle and look somewhat appropriate for a middle school teacher, e.g., not a backpack, but a large purse, messenger bag or tote would be fine. Lightweight would be great, if possible. Any suggestions? Thanks SuziAck