Some of the things I used to see while commuting on 295 south through NJ from Princeton area down a little past Cherry hill, against traffic, so usually 60-80 mph to keep up.
One of the local food stops starting doing breakfast bowls, we would see lots of people with bowl of hot food on lap held by one hand while using a spoon or fork. That place stopped selling bowls of food a short time later, Many, many accidents later.
Reading books, many, many times.
Even a few writing on a notepad, diligently.
Watching videos or doing video calls with the phone held on top of steering wheel.
So many people shaving and/or applying makeup, many times with the sun shade mirror (sun shade down).
What I call swingers, they enter the highway and immediately get into the left hand lane (3 lane highway), while still coming up to speed, causing many brake tests.
but my 2 constant favorites.
1) people zoning out and almost missing their exit. Almost every day there was a car or truck on it's side on the exit ramp.
2) bumper following at 80mph.
Best one was someone following so close that when the person in front had to slow, the follower went into the grass median, spun 360 and ended up facing back into the direction of traffic.
At which point he got back on the road and started tailgating again!
And of course the next time he hit the brakes hard enough to smoke the tires, even with ABS (newer car).
At that point when traffic was fully up to speed, he started tailgating another car, at which point I lost site of him.