Film windows. So helpful when shooting lots of different cameras and films. Love the slits on the back for 35mm, and good slide open windows on 120/220 cameras(so you can see the backing paper type).

Centered tripod mounting holes under the lens at the film plane. So many have them on the right or left side that need a special bracket or grip attachment that has it in the center.

Spot meters, I wish all my cameras had them so I wouldn't have to carry my handheld one around.

I don't care much for the shutter locks but do use them when they are available. I try to not put away or store cameras with the shutters cocked.