Have replaced the water pump and main electric cooling fan. Ignition coil and plug wires.
The A/C didn't work when I bought the car. I drove it that way for a few years, and decided to have the A/C system checked and filled. Shortly after I did, the A/C compressor seized, but fortunately the A/C clutch disengaged so I was able to still drive the car with the bad A/C compressor on the car. I ultimately purchased a rebuilt compressor and condenser as well. However I never had the system charged again, as I don't mind driving the car without air conditioning. The A/C compressor bracket cracked, and I purchased a used one at the Carlisle Corvettes show.
I replaced the valve cover gaskets (the car still leaks oil from the valve covers) and replaced the radiator as well. I cleaned 20+ years of leaves and other debris that accumulated at the bottom of the radiator and inside the fan shroud. I've replaced the fuel filter. I've replaced both rear wheel bearings, one of the drive axle (half shafts) universal joints, as well as a few rear sway bar link bushings.
I replaced the interior carpeting with OEM style MAS back carpeting and did my best to repair the interior door panels (they've cracked with age as the plastic gets increasingly brittle). I installed heat shield and sound deaden-er beneath the carpet. Corvettes are known for transferring a lot of engine heat into the driving compartment. Even with the insulation, driving on a hot summer day can be uncomfortable.
I've never had to replace the brakes or shocks, but have had to adjust the parking brake mechanism. I also replaced the frame for the rear storage compartment wells as the frame had broken due to brittle plastic. Previous owners recovered the seats with cheap vinyl seat covers, but since they're still in good condition and quite expensive, I never replaced them.
In the 15 years or so before I owned the car, it had been in the possession of 4 - 5 other people... and it wasn't well taken care of. The floor pan at your feet is cracked, as someone drove it over bumps or through an automatic car wash. I've patched the cracks with roofing tar to ensure it remains water tight.
I've replaced the power window ribbon belts on both sides and the passenger door power door lock actuator. The window & windshield weather striping leaked very badly when I first bought the car, and I was able to successfully stop the wind shield leak and all but a few drops of water from the windows (it's definitely a fair weather car). Most of the window weather stripping needs to be replaced as it's cracked and brittle with age.
I replaced the fuel pump twice since I bought the car, but the best thing about C4 vettes is the ease of changing the fuel pump, since it can be reached through the fuel filler opening. I've replaced various interior missing or broken plastic trim pieces, as well as trim screws and rubber bumpers (such as for the rear hatch window and the fuel filler door).
The radio reception was very poor when I bought the car, and remains so today. I pulled the interior dash cover and installed dash mounted speakers. I've rebuilt/repaired the power antennae as well.
I've replaced the interior dash bulbs (very expensive, hard to find mini bulbs... don't go to a dealership for these as they're approx $25+ dollars per bulb... a good auto parts store should be able to order them for you).
It left me stranded twice in all these years. One time for the bad fuel pump (and I got taken by the shop) and the other time when the ignition cylinder locked. As it turned out, the cylinder locked, because the bolts that lock the joint together, which allows the steering column to pivot/adjust, loosened. When that occurred, the steering wheel flopped around and allowed a spring inside the steering column to dislodge and come to rest in the ignition cylinder mechanism... which in turn locked it, and prevented the car from starting.