While asking what are "Must haves" could garner interesting items and personal opinions, I'd have to say the items below would be on most people's list.
- GOOD set of tires for each season. (good snow tires, grippy summer tires)
- GOOD forward lights (either HID retro's, Lightbar's, etc... something for dark winter driving)
- AutoStart for warming or cooling it
- ClearBra if newer.
Other things like block heater, tint, stereo, suspension, yada yada is more situational where everyone might have their own need/opinion. IMHO..