" It would not take too long before the people are being starved out. "
I've thought about this at length.
I have a "hobby farm" and I'm surrounded by the same, as well as Farms that operate as a full time business
and ranches with thousands of head of cattle. Plus I'm one of those "Prepper" types.
Tools, food, water, et al, survival stuff.
The problem as I see it is the towns, where people can't/won't do that sort of preparation.
Lucky the BI has a small population that is concentrated in a few towns, very far apart in very challenging
terrain. I'm sure I will live in 18th century style with no problem.
Oahu isn't so lucky.
No offense to Oahu guys but Honolulu will not be missed.
If everything goes the "A Canticle for Leibowitz" route you have what you have.
Good luck and God speed.

The problem with having a garden and knowing how to hunt & clean your game is you are competing with others. Your crops take time to grow. Once a crop is harvested, how long will that last for just one person? For three people? A dozen? How many are you going to share with because you have family or friends that have nothing to eat?
Then there's the need to have that dozen people in your group so you can protect what is yours. It's a symbiotic problem: are they contributing to the growing,, harvesting, scavenging, cooking and protection of YOUR food? If not, do they qualify to partake? Are you running a charity for those who CAN'T contribute?
When the shelves are bare -- at the stores, restaurants and your cupboard -- and the animals have been hunted out, how will you get what you and your group need? Fish? That's always a good plan, if the fish cooperate.
You will eventually become the group that takes from others, just as you defended against those kinds of groups in the beginning.
Being a "prepper," you'd need to plan for X number of days with food and water enough for Y number of people. If that means stocking up on pallets of MREs and cases upon cases of SPAM and wheat, canning what comes out of the garden each year (which only stores for a year or two if you're lucky), and raising livestock for milk, butter, eggs and meat, that's a whole lot of work and resources to prepare for something that will likely never happen.
IMHO, you either have to live the life as if you're already required to be self-sufficient, or you decide how much is enough for a short-term emergency. Anything else is going to be a losing proposition from a cost/benefit perspective. Hopefully living that life now helps answer the question, "Will I have enough for all the people I will depend on?"