Start by replacing plastic in the trays with upcycled ocean plastic that funds more ocean cleanup. Easy first replacement. See ogoori.eco for details.

Issue extra bonus and level points to passengers who decide opt out of their included meal ahead of a flight.

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

Using hydrogen tanks in the rear of the plane, for example. This could work on shorter routes such as domestic flights or intra-Europe.

Replacing the paper catalog with a QR code sticker. This saves tons of paper. Many catalogs are destroyed or unread.

When the crew collects trash before landing, why not make separate rounds for collecting, cans, plastic cups, paper, etc instead of collecting all trash in the same bin.