Antibacterial wipes, for cleaning without water. We don’t recommend using these in general, as widespread use leads to super bugs with high resistance to antibiotics. However, if you don’t have any water, the more important issue is fecal-oral contamination. After a major earthquake we will need to take extra precautions not to get sick, and make a difficult experience even worse.
If you are building your own bag, you don’t need to overload on these. Just include what you need to get home, and focus on storing plenty of water for cleaning up after that.