I'm not a fan of carrying loads on my back while commuting, but if all you need to carry is a tablet, I would consider a small lightweight messenger bag. If you are carrying other things and are asking about how to protect the tablet, I would just put it in a pannier with everything else. You would probably want some type of case for the tablet, neoprene or something similar. I carry a laptop in a pannier everyday with no adverse affects to the laptop.