I just finished a tour down Baja California, and am going to continue traveling in Latin America sans bike. If you would like to put my "Tidy Cats," or recycled kitty litter buckets made into panniers, into good use, I would be so happy! I know it sounds weird that they are kitty littler buckets, but they only held CLEAN unused kitty litter fresh from the store, they are waterproof, double as benches, critter-proof food containers for when you're camping, are SUPER bright and visible when you're on the road, and I am convinced they have a litany of other uses... They also have reflective tape on the back.
I don't have a photo of them but I found a photo of the buckets I used, and here is the link of where I got some ideas for building them so you can get an idea: http://www.instructables.com/id/Building-Better-Bucket-Panniers/
I am currently in Oaxaca (city) but will be in Mexico City D.F. maybe later this week, and would be happy to bring them there if it means that they will go somewhere other than the landfill.