It seems like every time I work on a project, I learn about another "bread-and-butter" component that I ought to keep plenty of on-hand. I wonder if there would be interest in sharing examples of people's favorites. I'd like to take as granted that one should have a variety-pack of resistors and capacitors, and focus more on ICs. Is this even a list that is worth compiling, or is it the kind of thing where everyone's list will be a little different depending on what they do?
Some things that come to my mind:
PNP and NPN BJT transistors. I have always used the PN2222 and PN2222a, but there are probably better, more modern choices. You can't beat the price.
555 timer IC.
A general-purpose op-amp. I think the LM741 is the old standby, but I have heard some people say it's dated, and there are much better options. Sparkfun sells the LM358, but I'm not familiar enough to judge. The 358 appears to be rail-to-rail, which si a good thing.
Opto-isolator/coupler. I use the LTV816, because that's what Sparkfun sells and I figured that means it can't be too bad. It doesn't have an accessible base leg, and it's not particularly high-speed, but for many basic purposes, I think it works well. When I first got into electronics, I didn't appreciate the benefits of galvanic isolation; now I live by it. Mis-matched grounds and unintended impedance interactions are the bane of my existence.
I have found good uses for a solid-state relay when replacing manual switches with computer-controlled ones. The relay's usage overlaps a little with the opto-isolator, but a main advantage, IMO, is that they can be purchased NO or NC, so that you can control what the relay's state will be when the control circuit is un-powered. I don't think you could have a NC optoisolator. I like the CPC1218 (Normally-Open) and CPC1219 (Normally-Closed). One nice thing about these is that they are entirely self-contained, so there is no need for supporting hardware like a current-limiting resistor on the control circuit. This is a good thing if you, like me, have a habit of accidentally blowing up your opto-isolators by accidentally forgetting the current-limiting resistor.
I would love to hear anyone's feedback on other "fundamental" components, as well as any feedback on better parts than the ones I've listed above.