I've discovered that every time you donate Med-X, Fixer or Rad-Away to Julie Farkas at the Old Mormon Fort you get 30 XP. You can actually buy the stuff from Julie and donate it right back to her, and level up on the spot until you exhaust the Mojave's total Med-X supply. Is this XP bonus a bug or is it intended this way?

Its not unlimited eventually she stops accepting meds one by one.