Great 4k monitor, can be flipped 90 degrees to code in vertical mode. Super useful.
Great mouse fully wireless, with smart gestures & high portability. Battery life is really long and charging is relatively fast. The only downside is that the charging port is located under the mouse which makes it unusable when on charge.
Keyboard with Apple keys & shortcuts. It's just a little better than using the laptop's keyboard. It prevents having a bad back position which might trigger backhache during long working sessions.
Probably my favorite investment ever. Sound quality is amazing. Noise cancelling tech is great, especially in environment with constant background noise (i.e. plane, train, car as a passenger). Probably increase my productivity just by wearing these.