Marcal paper towels (available at Staples) are 100% recycled, a large proportion post-consumer, and they come in the half sheets. The TP is a little rough, but it's fine for me. As long as I don't have food poisoning (ok sorry TMI).

Yeah, canning. I like to have home grown and home-preserved produce, but I'm under no illusions that home canning is environmentally friendly. The energy inefficiency is pretty much staggering, actually. A couple of paper towels to wipe the jar rims doesn't amount to much when you're leaving two burners on the stove maxed for four or five hours... never mind the water consumption.