What is a good small bicycle bag to store your gear and/or personal things? I'm looking for one that attaches to your bike and easily detaches so you can take it with you.  I usually ride with a small Timbuktu messenger style bag (really small, it's about the size of a large book) and I carry my wallet, phone, keys and stuff in it.  Is there something for bikes so that I can easily attach and detach from the bike?
Saddle Bag



It may seem too small at first. But check what I can fit in with my Specialized Saddle Bag:


Two spare inner tube boxes
Cell phone
Keys
Money
Train travel card
3 tire levers
Small toolset