Well the US isn't setup for it in most places but in larger cities it is possible although sometimes less convenient to take transit or bike, so I don't think people "need" gas to survive.

Even if you're not put fully out of work if you have less money you'll only take essential trips reducing gas demand even if you're somewhere without public transit at all. Same with food, less money means you'll buy cheaper alternatives that are generally easier to produce.

Just because something is 'essential' doesn't mean you'll always spend the same amount on it regardless of your economic situation.

I people are not on a fixed immutable diet and routine.

I would not put instant ramen and a steak in the same "food to survive" category.