Rule: Item has to be under $4 - a cheap, basic fast-food item, not some highfalutin 5 Guys burger which requires an entire cow to make, or some fancy-pants Chipotle burrito ("what's your protein?!") and guac (in case you don't know, "it's $1.80 extra, is that ok?!").
4. Chalupa - ground beef or chicken; steak is a bit iffy.
3. Chick Fil A Spicy Chicken Sandwich - not normally a pickle fan but it works here. CFA also has good service, although the "my pleasure" thing gets annoying, especially since everyone else is saying it now, too.
2. McDonald's Fries - horrible for you, but horribly good. They cost less than the teaspoon of guac they give you at Chipotle.
1. Egg McMuffin - as Yglesias said, "asking whether you could make a better breakfast sandwich than the McMuffin is a bit like asking whether God could make an object so massive he couldn't move it."