Shift knob. My Bronco had one of those chrome t handle jobbies. The chrome was starting to flake, it put my hand where my middle finger stuck out down the shift lever when I grabbed it, and was generally unpleasant to the touch. I got a factory knob from a junkyard. It is round, easy to get my hand around, is warmer and colder than the metal t-handle when the weather is cold or hot, and had a generally pleasant texture.
Since it is the thing I interact with second most after the steering wheel, it makes a huge difference in experience even though it is a small thing.
I also got serious mileage from door hinge pins/bushings, striker bushings for the doors and rear seat latch, and window seals and cat whiskers. My doors, windows, and rear seat would literally sound like the truck was falling apart. Just getting those under control was a massive improvement.In terms of most to least cost effective:
12* timing bump
Door striker bushings
Porterfield r4s pads and shoes. Stops on a dime even on 35" tires.
Electric fan conversion.
Proper Tires for my needs