Brown ground beef in batches, breaking it into small crumbles.
Drain fat well. Add taco seasoning and water according to packet directions, then simmer until liquid is absorbed.
Transfer cooked taco meat to slow cookers set to Low or Warm.
Set out Doritos bags, lettuce, sour cream, cheese, salsa, and any extra toppings buffet-style.
To serve, lightly crush chips in the bag, tear open the top, and add taco meat and toppings.
Serve immediately while the meat is warm and the chips are crunchy.
Notes
Drain the beef well so the walking tacos are not greasy. Keep taco meat warm in a slow cooker for 2 to 3 hours for parties. Taco meat can be made up to 2 days ahead and reheated with a splash of water or broth if needed. Set up two topping lines for large groups so guests move through faster.