How about luggage weight credit for airline baggage? If a passenger is underweight in luggage (or has only carryon or one bag) then they should be allowed to sell the weight credit and the airlines should be algore forced to accept it.
(I still want dessert credits. If I buy the dessert credit from someone who did not eat their dessert, I will get a guaranteed no fat sweets credit.)
What about no luggage at all? Trouble is that tends to raise eyebrows with the TSA and you get a spanish inquisition...which of course no one expects.