The toppings that belong on a street taco and why
At a good taqueria the toppings are: raw white onion finely diced, fresh cilantro, lime, and the salsa of your choice. That is the complete list for a street taco. The restraint is not minimalism for its own sake — it is because each of those components does something specific.
Raw onion: crunch, sharpness, a slight bitterness that cuts the fat. Cilantro: volatile aromatic freshness. Lime: acid to finish. Salsa: heat and complexity.
Everything else — sour cream, cheese, lettuce, tomato — is from a different taco tradition. Not wrong, but not street taco. Adding all of them to a street taco does not make it better; it makes it a different taco with too much happening.
