The Mission burrito is the build that added rice to the burrito, and that single addition is what makes the rest of it possible. A large flour tortilla is loaded with rice, beans, meat, cheese, sour cream, and salsa and rolled into a heavy, sealed cylinder, then wrapped in foil. The rice is not filler; it is the moisture engine of the whole structure. It absorbs the liquid from the salsa, the beans, and the meat that would otherwise pool at the bottom and blow out the seam, which is what lets a San Francisco Mission District burrito carry that much wet filling and still be eaten end to end from one hand. The defining decision is volume managed by starch: a complete plate of food sealed in a tortilla and engineered not to fail.
The craft is in the roll and the foil. The tortilla is oversized and warmed on a flat-top so it goes pliable and will not crack when it is folded around a load that would split a cold one. The fillings are arranged in a line rather than mounded, so the burrito rolls into an even cylinder where each bite reaches all of it instead of hitting a slug of rice at one end and meat at the other. The bottom fold is tucked first so the base is sealed against drips, and the whole thing is rolled tight enough to hold its shape under its own weight. The foil is a structural component rather than packaging: it braces the cylinder, holds the heat in, and lets the eater peel it back in stages so the burrito stays intact while it shrinks. The salsa and the sour cream supply the acid and the cool against the rice and the meat, applied inside where they can do that work without soaking through.
The variations are mostly fillings and one regional fork. The protein moves through carne asada, carnitas, al pastor, chicken, and a vegetarian bean build; a wet or smothered version ladles sauce and cheese over the outside and turns it knife-and-fork. The Mission's own offshoot folds in french fries to make the California burrito down the coast. The plain taqueria taco, the torta, the quesabirria with its dip, and the arepa are all distinct builds in the same flexible-bread family, and each of those deserves its own article rather than being crowded in here.