KOT did list a necessary tool. Anyone who deals with cover plates will, sooner or later, have to use a 3" 6-32 screw to hold a switch in place because some idiot put the electrical box behind the drywall. Or some stylish goof then put 3/4" T&G over the drywall. It's the kit from KOT's first link. And this doesn't get split up: keep it in the box.

I've occasionally had a need for the 8-32 screws, but there are a lot of other screw sizes that I commonly use. If you haven't already settled on other screw sizes, this might be a good place to start.

What this all comes down to is that if you buy a ready-made "kit," you will carry around a lot of sizes you don't need, and will learn from that what you don't need. I have a couple of plastic cases of stuff like this that I hardly ever touch. If you already have an idea what you need, go buy hundreds of those!