Why fast food is best start? Number one reason is no one wants these job and when one take these jobs, whoever takes these job would prove they wanted to work. Most employer would rather hire those who really want work and is currently working.
How about this?
WWOOF around the world
Click on one of the three links under United States. These are volunteer opportunities that could lead to employment of some sort. I suggest this over fast food for a couple of reasons. One, when S-is going to-HTF, where you going to get oil/coal to run the powerplants that supply electricity to the fast food junk joints in the big cities as a result of the US Dollar losing its world reserve currency status? You have to remember that you would be serving food to the very last person in the entire chain; the consumer! You would be losing a substantial customer base who no longer can afford fast food (or any food for that matter - look to Zimbabwe and Greece for today's examples of monetary policy run amok). Two, you would be developing and growing much-needed skills as a farmer. Without farmers, a country doesn't survive and becomes reliant on foreign countries for food, especially if future generations of both countries should become hostile and hurt trade relations. At least, SOMEONE is going to be buying food off of you, whether it be expensive restaurants still able to continue to operate under these circumstances or the people living down the road from the farm. AND you would be safely out of the way of millions of people coming out of the big cities in the scramble for food and safety, IF you are far enough away.
I'm considering looking into wwoof next year, starting to look in late winter. I encourage you to find something, as you might find something.
A fast food joint would be the last possible place I would look to employment. Remember, you're breathing in all that grease that is aerated into the cooking room... If SHTF personally for me, I'd be at a farm the very next day, didn't matter where I was. I'd rather be out of the city and outside in sunshine than the other way around. People don't know what they're missing. I've been living in big cities for the last near-30 years, and I'm tired of it. I hate it here, and I'm looking for ways to get out.
Good luck! I realize it's a tough environment out there. You might even have to work under the table and start your own business in the black market. Every time gov't tries to regulate businesses more and more, the bigger the black market grows. It ALWAYS happens this way. Consider that you are in a worker-hostile and business-hostile environment in the US.