Leave meat in whole pieces; you may even put it in frozen. In the morning, put the meat into the crockpot, add taco seasoning mix, and water. Plug it in and turn it on simmer according to manufacturer's directions. If you have time in the morning, shred the cheese and lettuce and chop the tomatoes and store in containers in the refrigerator.
When meat is cooked, remove with slotted spoon to a platter and allow to cool enough to handle. Place chicken breasts or beef on cutting board, and using a fork, shred the meat, while discarding any pieces of fat, etc, that you find. Return shredded meat to crockpot. Warm refried beans in small sauce pan or microwave. Wrap tortillas in foil and warm in the oven. Put remaining ingredients out in dishes on table. The diners can put together their own soft tacos or burritos with the ingredients they like best.