Okay, so cyanoacrylate adhesive, "superglue!"
It's some really good shit but a lot of people misuse it.
CA works best when the surfaces are nonporous and closely mated. It's awful at even the slightest gap filling so don't use it for that. It can also be brittle so be careful what you use it on.
CA cures from contact with water vapor and hardens in the tube. Even when I've been using it regularly I've always had tubes go hard before I used it all, so buy the smallest ones you can.
One non-obvious thing I find it useful for is tacking parts in place for me to then go over with a more structural adhesive, e.g. a slow-curing epoxy.
Superglue can also seal cuts, in a pinch! The thing where it cures instantly on contact with skin is helpful here.
@starkatt bonus: cyanoacrylate is really fun to say
@starkatt Octyl cyanoactrylate is actually used in medical care as a less invasive form of stitches! The ethyl cyanoacrylate that you get as superglue isn't as good for that though, because it's a little more toxic (though still not that bad; definitely do use it if there's an emergency!)