Cheap food is easy to come by in Cairo.
Here's a few recommendations:
Gad - This chain is all over Cairo and it's very popular. And cheap, too! There's usually a shwarma stand right on the street level with a walk-up counter to order your food. You can also go upstairs and order from a menu but the prices will be slightly higher and don't expect to get a cheap falafel sandwich up there. The food is excellent. A falafel sandwich (pita) is only 1.5 Egyptian pounds.
Felfela - There are two Felfelas. One is a takeaway restaurant similar to Gad; the other a sit-down restaurant. Takeaway is cheaper and they have standing bar tables you can eat at. It's not quite as cheap as Gad, but just as tasty.
Koshary stands - There are lots of koshary stands throughout the city. Koshary is a very Egyptian dish and it's delicious! Pasta & rice & noodles & tomato sauce & lentils & spices. Yumm! It sounds like a smorgasborg of leftovers, but it's surprisingly good. And very filling for usually just 5 Egyptian pounds (more if you add meat).
There are a lot of other cheap street food options in Cairo. Don't be afraid to try them out!
Written and contributed by travelsofadam