1. Keep doing objectives until you reach the "Sell 1 Weapon or Outfit" AND "Equip 1 dweller with an outfit"
2. DO NOT COMPLETE the aforementioned objectives, if you do you will be unable to do this glitch
3. Complete the remaining objective over and over again. After a while you should recognize a pattern
4. You will likely receive 2 lunchboxes per "cycle" and you can open them up whenever you want