How Cheap
Look, 100 years ago, you could buy a loaf of bread for a dime. A quart of milk for a nickel. Times have changed. But I think there are 4 "low-cost" barriers that are worth exploring in NYC. Outside of NYC, these might be even less expensive, but there's the intrinsic cost of transit to get to these places that doesn't really exist as much in NYC since you can get most places on foot or on a low-cost subway/bus ride (free, if you have an unlimited metrocard) or with a CitiBike membership ($200/year, unlimited 45 minute rides, or buy a bike for $180 and a $20 lock, same difference).
The barriers are somewhat arbitrary, and of course, the idea of low cost varies from person to person. That said, everyone would agree that if you can maximize $5, you are in good shape, and if you need to squeeze down to $3, there are still choices. So, those are first two dividing lines. Then $10, and finally $15. While $14.95 might be a lot for many people, you can sometimes get an incredible deal, enough to take home and have a second meal the next day, thus, under $8/meal.
Step 1 is to download all the apps available for food related things. McDonalds, Wendys, Burger King, White Castle, Dunkin, Starbucks, Chipotle, Boston Market, and basically anything else you can enjoy.
Under $3 (Maybe $3.25 After Taxes)
At 2 Bros Pizza (and countless other dollar pizza places), you can get 2 regular slices and a soda for $3. This is getting a little harder to find as a deal, and often the soda pushes it to $3.50. I am still including it here, average it out with the Wendys Kids meals. There are still a few 2 Bros in the city, 40th and 9th, 30th and 8th, 26th and 6th, and probably a few others. And nameless dollar pizza places are everywhere. Don't expect any toppings at these places, those add at least $1 to each slice, if not more.
Breakfast carts will give you a bagel or muffin and a coffee for $3 especially at the end of their shift.
Wendys has a breakfast meal for $2.99 for now. Comes with potato wedge fries and a coffee.
McDonalds has a dollar menu, as it has had for many years. You can get a large soda for $1. Four piece nuggets are usually $1.
At Wendys, after 4pm, Kids meals are $1.99. That means you can get fries, a drink, a toy, and a burger or nuggets for $2.17 and have $0.83 to spare. Also at Halloween, they have $1 booklets of frosties and around Christmas, a $2 keytag that gives you a free junior frosty with any purchase for the entire following year. These are obvious slam dunks.
Under $5 (Again, $5.40 After Taxes)
Wendys has $4.44 meals, $5 biggie bag meals. These are pretty big meals. They have a burger, nuggets, fries, and a drink.
McDonalds has a $5 meal deal of a small fries, 4 nuggets, small drink, and either a double cheeseburger or McChicken sandwich.
You can definitely find pizza places in this price range that will give you 2-3 regular slices of pizza and a soda all over the city.
Dunkin has tons of great deals - for $5 you can definitely get hash browns and wraps, or a medium coffee and a donut.
Up to $10 ($11 After Taxes)
This is where I can finally recommend Chipotle. A kids meal here is pretty great if you go meat on the side and get a cheese quesadilla and chips and a fountain drink. Almost always enough.
Boston Market has a great kids meal. And you can usually get a buy-one-get-one deal for the following Saturday with that purchase. Come back Saturday and find a $9.99 meal and get two! If you can find a Boston Market that has not closed down, that is.
Up to $15 ($16.50 After Taxes)
Mad For Chicken has individual meals that are great - many flavors of strips or wings, and some of the best fries around.
Qdoba is not bad, similar to Chipotle.
Five Guys makes great burgers and fries, but also hot dogs.
Shake Shack makes great burgers and fries, but also hot dogs, and of course shakes.
Your local Chinese food place. Try a bunch to find the one that works for you. Lunch specials are usually $11-$13. I love Ollie's, there are a few in Manhattan.