The note is a photostrip of the pharmacist and his wife/girlfriend, Laura. It shows a collection of four images taken in a photo booth from "Sharesnap." On the back, it is a note from Laura that says,
Think about me while I'm off. I'll be missing you, but not too much. --Laura
It can be found in the back of the American Princess store, where the pharmacist can be found dead in a bunch of fungi. After Ellie loots the Pharmacist Key off of him, you can then pick it up.