Here is what I have for two scenes that could be included somewhere along the roadtrip. It's pretty much just a rough sketch of an idea. I haven't thought it all through but I wanted to get these ideas down before I lost em and I figure you'll all have some ideas so here's what I've got.
So far I was thinking about a scene (or two) that would play out somewhere along the road trip. It would fit in at a point when the zombie problem is becoming more apparent to the protagonists, maybe somewhere that the bear can be included (a state in which they are indigenous).
First you have a scene where a lone hunter pulls into a service station for some gas, his latest kill (a bear) is in the truck bed. Instead of lone hunter it could be some kind of wildlife ranger with a bear he had to subue/relocate, whichever works best. Nothing much happens in this scene except a talk between the ranger/hunter about bringing down said bear and the odd conditions it was found in (eating another bear or some other kind of zombie animal like behavior, attacking campers and whatnot). The ranger/hunter scene ends with the man paying the attendant and heading for the door back towards his truck.
The next scene shows our HIC road trippers having abit of car trouble. They'll need to stop for gas or maybe a part to fix something that is failing on the truck (a hose or some such). They pull up to a rather familiar service station and it is apparent that there is a zombie presence (mauled corpse/s, dead ranger/hunter, blood on stuff etc).
Dialog:
"Man, we can't stop here, this is zombie country"
"Indeed,” (Grinning, offering a kukri)
(Grininng as they exit the truck) “A Bonecutter eh? That's fitting, but if you let me get eaten I will haunt you good, so good..... you'll wish I didn't haunt you so good.”
“Ooo scary, and here I was planning on leaving your slow ass for the undead should things turn south.”
“Well if you do that, your gonna have to live the rest of your life with this mug (makes face) popping out every time you sit on the john or make love with a women.”
“I'll bet you want to watch me on the toilet, you sick bastard”