Let's start by using SAF at least for domestic flights.

Long time ago SAS had a shared limousine service in Sweden. For a resonable price, a stretched Volvo picked you up, and a few more passengers.

Encouraging standardized suitcase measurements and/or using AI to plan and stack luggage for saving space and even out the plane in regards to weight.

Mount small blades on the side of the wheels to make them spin by themselves before landing to reduce tyre wear upon contact with tarmac.

Offer an educational series during the flight about climate change and what passengers can do to help.

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