As you'll notice, one day you are going to breadboard something to test things out, just to find that you don't have
that most stupid component that is really needed for your build.
Even worse, you don't have anything to replace it with.
So what do you do?
YES, you build up a stock of some common, cheap components.
Note that buying components from ebay, aliexpress or any other Chinese vendor does not guaranty you to get official components. If you want the real deal, and not knockoffs, you'll hve to go and buy them from reputable sellers, (localy, of on the world wide web). Some examples are farnell, mouser, conrad, digikey, and many more. (note that in some cases you can't buy if you don't have a company of some kind, or at least a VAT number).
Well, how do we build up stock?
That is up to you. There are 2 ways to building up stock:
1- Buying a whole lot of stuff at once that you think you could have the need of in the near future. 2- Buying excess when buying for your projects.