Make a “code-share” cooperation with train providers, to allow for booking a ticket from A to B with combined train-plane modality and same benefits as connecting flight

Serve sustainably grown coffee and tea on all flights from farms that are certified as carbon offset due to their farming practices

If you reduce the allowed weight for luggage from 23 kg to 15 kg or so, people might start to think if they really need all that stuff with them.

My personal CO2 emissions should be listed on my boarding pass in the app for each flight.

Almost all passengers have their own phones/pads these days. Keep them connected with *good* wifi and IFE wont be needed, massive weight savings.

When going from A to D some times you need to transit in B and even C. Price match the most eco-friendly with the cheapest alternative in points.