Mashed chickpeas with vegan mayo is a good approximation of a tunafish sandwich.

Op post a budget and how many days you need it to last. That’s far more helpful.

Also what do you have to cook in? Stovetop? Oven? Microwave? Air fryer? Crockpot?

We can be far more helpful if we know some details

Zero carb tortillas / pizza sauce / cheese/pepperoni is super cheep pizza.

Cast iron pan / fresh green beans / butter / garlic

Chicken / rice/broth soup

Rice is super cheap and can be used with a combination of ingredients. And makes quite a few meals. I miss being able to eat rice.

Zucchini sliced, green pepper, red pepper, onion, andoulie sausage if you can afford it. Coat in Italian seasoning or slap ya momma.

Air fry for 15 minutes. You can easily get two meals out of that

Tomato. PB. Egg.

Peanut Butter. As a diabetic it’s my go to when I want something sweet. As long as it’s natural.

Also I don’t know your kitchen situation but you can live off just Potatoes and they’re filling. Microwave, bake, or air fryer. They are awesome in air fryer.

But how bad off are you if you can’t even get cheese slices?

Like what’s your budget? How many days before you get paid and how long do you need a extremely tight budget for?

Toast sandwich

Peanut butter is one of the cheapest shelf stable foods, either per calorie or per gram of protein. It’s obviously delicious with some sort of fruit jelly/jam. And the protein in peanuts complements the protein in bread, covers all the essential amino acids.

Spreadable or meltable cheeses are pretty delicious on toast, and can be supplemented with seasonings. I put cream cheese and everything bagel seasoning on my sourdough slices most mornings.

There are also a ton of delicious toppings for open face “sandwiches” or toast:

1. Avocado is a classic for a reason. If avocados are cheap near you, that can be an option.
2. Fresh tomatoes on toast are a classic in Spain for a reason, too.
3. Sardines or other canned fish/seafood, if you like that.
4. Mediterranean spreads like hummus, baba ganoush, muhammara, harissa, etc.
5. Shrimp, like gambas al ajillo or something similar, go really well on toast.
6. Roasted mushrooms

If you’re baking your own bread, you can also try to shape some little bread bowls and fill them with soup. French onion soup takes some time but the ingredients are pretty cheap.

Not all of these options are ultra cheap, but many are flavorful enough that even small portions can work out to be really affordable on a per calorie basis, for stretching that budget with bread.

Peanutbutter and jelly.

Canned tuna is good and cheap.

Sweet pickles or barbecue sauce on the meat between two pieces of bread, idk it isn’t bad. Definitely poverty food though.

1 little can will get you 2 or 3 sandwiches, and a big can will get you like 7 or 8.

Not exactly what you asked, but there are whole traditions of non-sandwich food eaten with bread. For example, if you can get lentils for cheap you should look into lentil soup, and same for broad beans and ful. Also you can put a thin layer of tahini on top of molasses for a surprisingly tasty breakfast. You eat all these by scooping them up with bread.

This will sound insane, but it’s amazing. It’s a niche fast food in West Africa that I make myself a few times a year.

First, get some bean flour. Any kind will do. Black eyed pea flour is best, but it’s usually only something you find in an African food shop. Chic pea flour just as good, so is black bean flour.

Mix with salt, herbs, chicken bullion, and water into a dough and deep fry spoonfuls in a skillet into fritters.

Make up a batch of spicy tomato sauce. Lots of onions and oil and pepper.

Put those fritters in 6-10 inches (have someone else measure, guys) of the cheapest, thin baguette money can buy. Slather in sauce. Enjoy.

Entirely vegan if you want. Complete protein. Zesty, spicy deliciousness.

Online, look for kosai or chichena recipes for the fritters.

Peanut butter

Peanut butter! Cheap, high calorie, with fats and proteins to balance the carbs. You can get jelly packets or even ketchup packets in a pinch (not quite as bad as it sounds) to keep it from getting repetitive.

Also consider rice and beans!

Tomato sandwiches. Slice the tomatoes and season with salt and pepper and spread some mayo on the bread. Simple but delicious.