I too generally just plan ahead, see what I need for the modules I want to build, but always get extras — you never know when a part’s going to get fried or lost or something — with the result of ending up with a stockpile mostly of commonly used parts. After some time you get a feel for what parts you use a lot of and can stock up on them. It’s hard to get agreement on them, though, people tend to build different sorts of modules that require different distributions of parts.
I try to keep a few of most E24 resistor values, at least in the 100R–1M range. Some values I buy 50 or 100 or 200 of at a time, not that many though — yeah, they’re cheap, but some values you just won’t use 100 of. Likewise I buy lots of a few capacitor values and types (don’t neglect film!) I use a lot of but mostly I get them and a few extra on an as needed basis. Jacks definitely, and B100k and B10k pots — but not too many because there’s panel mounted, board mounted vertical and horizontal 9 mm and 16 mm, all in 6 mm or 6.35 mm shafts; expensive to buy a lot of each of those and then not use them. And I buy knobs in bulk. TL072 and TL074 chips (I have some TL071s but they’re not used that often), and LM13700 which you might have trouble sourcing in the future. 8- and 14-pin sockets. 1N4148 and 1N5817 diodes. 2N3904 transistors, and fewer 2N3906. Or BC547 and BC557. Generally you can substitute the former for the latter (turned around 180° though) and most other BJTs you see in circuits can be replaced with one of those. SPDT switches. 40-position pin sockets and headers to cut to length, 10-pin shrouded headers, 10-pin IDC connectors and 10-conductor ribbon cable. LEDs, I mostly use 5 mm green ones but if you’re using someone else’s panel you might need 3 mm and the color is a matter of taste. (No, I can’t taste color.) 2- and 3- position Molex headers and connectors. 24 AWG stranded hookup wire in a few colors, and some solid hookup wire — more of that if you do a lot of stripboards. I think that’s most of what I can reasonably count on finding in my supplies, anything else might be there or might need buying as needed.
Also see: