I tried smoking damiana once and thought it was pretty harsh and didn't taste good.
You could use catnip or something, it's also kinda harsh though, but less so than damiana IME. I've heard Red Rasberry leaf is good for making synthetic cannibinoid blends and smokes well and is pretty smooth, it'd probably work ok. Anything you add to the weed will fuck with the taste of the herb.
You could use a vaporizer or a one hitter to extend your stash. Or just pack smaller bowls. I assume you want joints or blunts though.