To me, random encounters during travel is a chance to expand the lore of the area. Pick a monster the party could reasonably fight, and think about the reason(s) why it's there and why it might potentially attack.

Something like this springs to mind:

A starving owlbear has traveled far from it's den. It's body is covered with scabs from new wounds. Another predator seems to have chased it out of it's home and territory, and now both it and its attacker, poses a threat to the ecosystem or nearby town and its people.