In my efforts to find the perfect cargo solution for me I've tried everything. Panniers, backpacks, messenger bag, etc. What I've been doing lately is using the panniers when I need more room (grocery or beer runs) and using my new messenger bag when my needs are less and/or I want to bring stuff with me after parking my bike.

I did pick up a milk crate but it won't quite fit on my rack right now as the rack is tilted somewhat forward and the saddle is in the way. I'll either have to trim off part of the crate or make something to extend the rack stays so it is back further.