Resistor selection, I have a few hundred through hole, and a few thousand 1206 size.
I keep the 1206's in 7 day pill organisers (4 compartments per day), the ebay selections etc I think tend to have too many, or too few, or not the sort of combination that would be "efficient", I only keep certain values which I selected myself....
1, 10, 100, 1k, 10k, 100k,
1r5, 15r, 150r, 1k5, 15k, 150k,
2r2 ... to ... 220k,
2r7 ... to ... 270k,
3r3 ... to ... 330k,
3r9 ... to ... 390k,
4r7 ... to ... 470k
5r1 ... to ... 510k,
1M,
120R, 180R, 240R, 300R, 360R, 430R (useful inbetweeners in the "typical LED current limiting" area).
The through holes are just some random sample pack, ebay, futurelec, somewhere like that.
Add some trimpots as well, up to 1k.
Capacitor pack, again, random sample pack from ebay, futurelec etc. Electrolytics and ceramic.
Linear regulators - 12, 5, 3.3 and adjustable, always handy.
Transistors/Mosfets - the transistor selections you can buy on ebay IMHO tend to have too many different ones, especially if you are mostly dealing in mainly low speed digital electronics, you might not find too much use for 80% of the pack. Here are what I have around...
100mA: 2n2222 (NPN), 2n2907A (PNP) - (SMD equivalent eg MMBT2222A, MMBT2907A)
10mA: 2n3904 (NPN), 2n3906 (PNP) - (SMD equivalent eg MMBT3904, MMBT3906)
Darlington Array - (available in SMD also)
2N7000 mosfet (N Channel) - (SMD equivalent 2N7002)
Maybe a few discrete power transistors and mosfets, but those are more the sort of thing you might get for a specific project (since they can be costly).
If you are looking at SMD, then I'd also suggest as potentially useful and cheap from china:
SS8050LT1 (NPN, 600mA - 1500mA), SS8550LT1 (PNP complement of that), SI2302DS (N Channel Mosfet), AP2305(A)GN (P Channel Mosfet)
Normal Diodes: 1N4007 (or 1N4004, whatever is cheapest on the day), 1N5819
Zener Diodes: Whatever you think might be useful, 5v1, 5v6, 3v6, 6v8, 15v
Light Emitting Diodes: A selection, through hole in 5mm and/or 3mm, and if you like SMD (1206 size or smaller).
ICs: 555 timer of course, H-bridge driver (L293D, SN754410NE or similar), shift registers (SIPO, and PISO), some LM324 or similar op-amps, a micro controller or two of your favourite breed
Hardware: tact switches (in various shapes and sizes), screw terminals, 2.54mm headers (single straight ones (you can use two togethor for doubles), and some single/double angled ones; in both genders). You might want to keep a couple of larger potentiometers, and toggle switches around too.