Pay for luggage by weight.

Even if you have a few seats in business. The planes will be filled as usual while providing better service with almost no additional carbon footprint.

Expand conscious traveler so that every 10 steps gives 5000 level and bonus points. Not only once a year. This will engage more people to engage in the program.

Invite all travellers to bring their own coffee cup.

Present sustainability data for the flight in the infotainment system, with for instance bio-fuel stats, # meals pre-selected and how much carbon emissions was saved.

Introduce a "minimal comfort" seating class with basic amenities and reduced seat recline, allowing more passengers per flight and lowering per-person emissions.