I miss the following:
Transmission dipsticks.
Normal sized (13"-15") rims.
Manual crank windows.
2-3 door cars. Why does every car have to be a 4 door?
Regular mechanical parking brakes.
Regular metal keys with regular ignition switches.
Manual climate controls / knobs for everything.
Enough extra space in the engine bay.
Spare tires.
Regular unpressurized coolant overflow tanks.
Metal parts.
Hatchbacks that are actual hatchbacks like my 1995 Escort. What's referred to as a "hatchback" today is really a small station wagon.
Regular serpentine belt with an automatic tensioner. A stretch belt is a deal breaker.
Oil filters in the metal casing.
Replaceable transmission filters (as opposed to the type that requires you to completely disassemble the transmission).
Reliable transmissions.
Regular light bulbs for headlights (not the $1000 - $2000 LED types used today).
Parts that didn't require a matching VIN to work.