Launch escape system
The LES is probably the single most important safety item of any spaceship.
It has saved lives.
I also think it would enable the crew not to have to wear a pressure suit on the way up or down from space.
Besides, after Soyuz 11, or even before (thanks the Shirra's stubborness) none of the Apollo astronauts ever wore pressure suits on their way back.
The problem would be to build a spacecraft for up to six astronauts and use a reasonably lightweight LES. There was that reconfigured Apollo capsule once, that could return 5 astronauts from space.
Raoul