I always take my plasma / BIP as my primary travel pair, mostly because I've got a large stockpile of backup BIP lenses; travel is a great opportunity to ding up your lenses and I don't want to risk custom cuts, etc. Then I pack a second pair for contrast / low light conditions, lately oo red polar.
I try to limit it to that, unless there's some specific travel activity (i.e. the beach) that requires me to bring additional o-matter pairs to avoid risking losing my Juliets (like what happened last year...)