Waking Up Dead (End of Days Love) by Emma Shortt

You know your life has hit rock bottom when you're living off cooked rats and showering once every few months if you're lucky. But for Jackson Hart things are about to get a whole lot worse. When her best friend, Tye, disappears hunting for food, kick-ass Jackson's head south to safety' plan looks like it's dead before it's even begun. But then she meets ex-mechanic Luke Granger, who takes her to his bunker, feeds her with non-rat based food, and offers her protection against the zombie hordes not that she needs it. She knows how to use a machete and isn't afraid to.

Jackson was tempted to stay in the city with her rescuer. Food, shampoo and the possibility of finally getting laid, what more could she ask for? But the flesh eaters are getting smarter and the bunker is compromised, so Jackson and Luke have no choice but to make the journey south.
Luke and Jackson team up to find other humans in a road-trip romance for the ages. They travel for thousands of miles with zombies shadowing their every move. They must utilize every resource at their disposal and then some. On the way, they discover that even if flesh eating zombies are knocking down their door, there's always time for sex and even love.