Ensure correct recycling of plastics by unwrapping meals and plastic protected crisp breads before handing to the customer.

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.

Implement sharkskin technology or (my own) coating to reduce air resistance and micro-drag from the fuselage.

Bio fuel / green fuel as default, and having to pay more as a passenger if you want to fly on fossil based airplane fuel.

More efficient engines using sustainable aviation fuels combined with optimised flight paths and reduced taxiing time. Only use digital tickets.

Use travellers feces from flights as a bioproduct. As fuel or to something else useful.