Achievements. Does anyone care about someone else's achievements? Do YOU check your achievement lists and go "oh yeah, I'm so proud of that, good memories"? The only one I ever tried was "carry the garden gnome through the entire game and put him in the rocket at the end of the game"-achievement for Half Life 2 Ep2, because that sounded funny. Until you realize the game is basically a long as drive through enemy territory, and your gnome will get flung out of your car every few seconds.
Mostly, achievements don't even deserve that name. They're more like milestones for statistics I don't care about.
Collectibles. I love exploring in games. I do not love backtracking for hours, because I always miss at least one collectible, and they're almost always useless and annoying to look for.
The new Thief game has these special loot items you can only look at in your hideout. Which sounds cool at first, but I did that once or twice and went "I put a crap ton of work in for THIS?".
For shooters, it's mostly satchel charges and tripmines. If I do place them, I probably just leave the area and lose them, or nobody will come this way. If they do, I won't see it in time. Mostly, I just use them if I'm out of grenades. Otherwise, I'll be too lazy to get out the detonator, and I will mostly time detonation poorly. As for the mines, they'll end up killing or obstructing me more often than enemies.
Sometimes, if I already know the game, I think I can rig enemy spawn points in advance. And then, they don't get triggered, they somehow don't cause damage or they disappear. These things never seem to work out for me.
Also, every game that features a swimming skill. Like Deus Ex. What's lung capacity good for in GTA V? For that one time I actually swim in water and decide to take a pointless dive? Yeah, like I have an hour to level that up.