I subsisted on Ramen and chicken pot pies because they were cheap (4/1$ for Ramen, 2/1$ for chicken pot pies). Even the cheapest dollar meal at the local fast food didn't have as many calories. But, no, I didn't worry about food all that much.
First thing is to learn to cook. It's generally cheaper to buy family portions and make your own than to buy individual meals. For example, a bag of rice is $10, but can act as bulk in many meals such as fried rice, chicken & rice, steamed rice with butter & onions.. Yeah, doesn't sound too appetizing, but it can be. Fried rice, for example, is easy to make. For about 20$ worth of ingredients, you can have 10 meals. Just need rice, an egg or two, onions, salami/pepperoni, etc.. You can buy a pack of miso for around $4. Add firm tofu ($3) or chicken chunks ($4) and dried seaweed ($3) and you can make soup for 10 people. Buying a bulk pack of 50 tacos will set you back around $10; add a couple pounds of beef (10$), lettuce (2$), cheese ($5), etc., and you can feed 10 people for $50 or so.
Next, use coupons and shop of two-for-one days. You can easily save 50% of your bill just by using coupons and shopping on the right days. Avoid individual meal items such as can soda and even White Castle burgers.
You can also show up at friends/relatives around dinner time but use that only as a last resort unless you're really tight with them. Make friends with someone who works at a pizza shop. I knew a guy in college who would take leftovers from the restaurant. At a Denny's, for example, he'd order a coffee. When people were about to leave he'd run up and ask if he could have their leftovers. Bizarre, but he saved a few bucks. He's also gotten pretty wealthy since those days so I guess it paid off. I figure that one day he'll find a way to end up in jail just so he could get a free meal and bunk. :/
Oh, and forget about corned beef. Back in my day it was cheap, around $1.50 a can. Now it's close to $6 a can. I remember many days eating corned beef and cabbage, corned beef and scrambled eggs, steamed corned beef, corned beef sandwiches. No more.