Let's see, my mods tend to be minor and mostly related to cabin comfort . . . but:
1. Upgraded tires
2. Good quality speakers all around
3. Wide-angle rear view mirrors
4. Rear view camera with powerful white LEDs in the rear turn signal housings for backing
5. Does glass-coat paint protection count as a mod?
I call these the can't-live-without modifications. There are other things I've changed or installed, but these five are the ones I say, "God, driving is so much (easier/safer/more fun) with these changes" every time I get in the car. I still long for a moonroof or a targa panel. You think I could do it with a can opener?