Film didn't make much sense to me

So the water would possibly run out in a matter of days during a major event. He was trying to save as much clean water as possible.

The wife was an odd one, but some people just snap and their fight or flight kicks in. She flew where the father decided to fight.

There isn't really a zombie scene. As the closest I can think of is just the cannibals but there is common information that if you eat brain matter there is a very high chance of Mad Cow Disease and that will eventually shut down your body. Or the people that were severely starved in the basement your just running on instinct if anything.

The heading for the coast was more or less the warmer weather in places like Florida compared to where they first started

Yes there was some weird story parts but all in all it does the job of a Father who just wants his Son to live to see another day.

the wife's fatalistic reaction seems very realistic to me. Have you seen some of the people right now who can't handle wearing a face mask during the pandemic?

There weren't any zombies

The coast tends to have more people who may be more trustworthy and resourceful as they have access to waterways and sea-based trade. Those living inland literally turn into cannibalistic Deliverance "crackas" on steroids

The story is about survival in a bleak setting and the experiences along the way. The child is the father's "god" so he must sacrifice his own life to save "god" in the end.