Rope on a milk crate. Line it with a plastic garbage bag.
It will hold two full (double-bagged) grocery bags. If you wanted, you could change the garbage bag
often enough to make it leak-proof, and twisty-tie it shut above a load in wet weather, though that
strikes me as overkill.
The flat back surface is perfect for a huge day-glow orange `slow-moving vehicle' triangle.
I have found that a cheap (eg. Bell) seat-post mounted rear rack, with plastic top removed, can
be put under a regular rack to stabilize it side-to-side, greatly increasing the load you can
carry easily. The load is carried by the regular rack but it's stiffened side to side by the
seat-post rack.
Put a piece of wood under the milk crate to spread the load, since it will hang off the back end of
the rack about half-way, with or without the side-to-side addition, since the plastic can't handle
the load otherwise.
--
Ron Hardin [email hidden]
On the internet, nobody knows you're a jerk.