There was a challenge floating around
a number of years ago wow, it was over a decade ago now - known as the
food stamp challenge. There have been a few more threads since. I found it interesting how varied the results are based on where you live and your family situation. I suppose it would even change over time. I would probably buy different foods now compared to then, partially because of how food prices have changed, and partially because of food preference change.
I think if I did it today, one of my preferred veggies would be either a head of cabbage or a bag of cole slaw mix if it was cheaper. There's so much you can do with it. I would probably buy basa fish since it's only 1.99 for (what I could stretch into) 4 servings - DH hates canned fish. Wieners, cheap lunch meat and buns (for DH) would be on the menu.
The hardest part about it for me would be the loss of freedom. If I want a LC treat, I can generally have it - I could make keto buns out of almond flour, etc - but that stuff is all expensive.
I went through a stint of poverty about five years ago. I was underemployed and could barely pay my rent. My saving grace was the fact that I was fed at work, and I got by with my food budget just being my coffee and cream, and weekend food - whatever was on sale at the walking-distance grocery store and dollar store. I was already pretty good at frugal eating. I'd make a recipe and freeze leftovers, so I always had a nice selection of frozen homemade food. It's not like I had to eat ONE meal repeatedly all weekend. So that's kind of a cheat to compare a $20-per-week budget. Most of my coworkers eat crap at work - heck, it's my job to MAKE the crap - but the food available is awesome if you make the decision to dig a little. We have lots of bacon, sausage, cheeses, a nice salad bar, and a stir-fry station with good veggies. Some of the meats are off-limits for me because they're not gluten-free, but I work around that.