For me I suppose the must have options are:
Sports Seats - much better support than the standard seats, especially on corners.
Sports chrono - with the various driving modes (normal, sport, sport plus, individual) it makes driving much more fun. The normal mode is great for driving slowly around town. The sport mode is great for driving quickly on regular roads. The sport plus is great for track use. This option makes the car much more versatile. ALso you get other extras like dynamic engine mounts, etc.
Heated seats/steering wheel - it gets cold in the winter!
GT steering wheel - the smaller size is a better fit for me (and it looks cool)
Those are probably the only must haves. I got other options as well, but they weren't must haves - they were just nice extras.
2017 718 Cayman S
2008 987 Cayman S
2001 986 Boxster