Frequently people address my backpack. This appears somehow funny to me, like telling a motorist that he has got an awesome trunk.
A couple of years ago I got myself an Ortlieb Messenger Bag and this is what it says in black letters on orange tarpaulin. Hence many cyclists mistake me for a bicycle courier.
The really loud color makes be being seen and tarpaulin -- in combination with the ingenious roll closure -- makes it water proof (tested under the shower) and easy to clean. With a capacity of 30 liters it is large enough for weekend trips and most shopping tours. Still comfortable to wear when it is fully packed it meets my needs almost perfectly. The only thing I miss is a hand strap. I think that some of the newer models feature one.
What else could one ask for? Anna criticizes the lack of different compartments. I don't miss them, but Ortlieb offers inner pockets, dividers and other optional accessories.