Giving an incentive and getting more passengers to travel light should reduce aircraft loading and fuel consumption. Alternatively allow more cargo.

Reusable coffee cups for take away coffee and in-flight.

Develop incentive programs for staff to contribute ideas on reducing emissions. Make staff applicable for perks by doing "missions".

Only fly when tailwind

A lot of ground equipment is still driven by internal combustion engines, and can be upgraded to run on electric instead for better efficiency.

Taxiing from and to gates from runways should be more smooth and with less fuel - using for example AI