Make more out of every trip - it's not all about reducing the emissions but making every trip worth it. Sustainable travel is when the trips you make are worth it.

Offer Eurobonus points to passengers who order vegetarian/vegan food in advance

Use modern IT to implement dynamic codesharing, providing an interline journey following an optimized flight plan, rather than a static agreement.

Finger food that's easy and clean to eat reduces the need for cutlery and packaging. That's less weight and packaging and opens up for fun, hearty snacks.

For hand wash tissues, hand out from a larger container instead of singles wrapped in plastic.

Find ways to allow tax-free purchases to be done in departing airport and to be picked up at the airport were I land. It could save a lot of weigh/fuel.