Pour boiling water into a thermos and let it sit for 2–3 minutes to preheat. Carefully pour out the water.
Heat the taco meat until hot. Transfer it to the preheated thermos and seal tightly.
Pack the crispy taco shells, shredded lettuce, shredded cheese, chips, and fresh fruit separately in zip-top bags or airtight containers to prevent them from becoming soggy.
Place the thermos and all remaining ingredients in the lunch box.