For folks who are concerned about transporting stuff, I sometimes commute to work on my bike and love, love, love my milk crate. It is way old school and my other bike commuting friends make fun of me - however they don't make fun when I bring in decorated birthday cakes or other goodies to the office...

Covered coffee works just fine with a small bungee cord to keep it upright.
If you want to set one up on your bike, just add a rear rack (mine is the one that came with our Rhode Gear seat for DS when he was small) and attach your milk crate with zip ties. The zip ties are nice because they are secure but temporary. So I'll take my crate off when we drive down to the Fort and just put it back on when we get there.