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.

Make the app as lightweight as possible. Remove images, animations and leave only the bare necessities. This saves data transfer and storage - which in turn saves energy.

Badges in app after booking bio ticket or SAF add on - driving positive recognition and repetition

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

Dedicated recycling bins in galley/ head for passengers to use during non-service times

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