How to stock up on Electronic parts and not waste (too much) money and your girlfriend's goodwill:
1. Buy a resistor kit from eBay. Buy additional 100x of 100Ohm, 1KOhm and 10KOhm resistors. If you ever need more resistors, say 2 for a project, buy 10, unless the value is in the E12 resistor series, then buy 100.
2. Buy a Capacitor Kit from eBay. The electrolytics in these sets should not be used in anything you want to last long. Buy additional 2200uF 50V and 4700 50V caps from Mouser for your power supply needs.
3. Buy a 1W Zener Kit from eBay (about 10 pieces per value)
4. Diodes: get 1N914 and 1N4007 (100 each). Additionally get some 35Amp hard core bridges (5 e.g.) for power stuff. Everything else should be bought from DigiKey or mouser in 10 quantities)
5. LEDs (buy 100-200 packs from eBay. They are dirt cheap.)
6. Buy TO-220 Regulators. 3.3, 5, 9 Volts. Buy 10 of each from a reputable source. Also buy a bunch 10 of LM317 and 337s. Also get a few low droputs like LD1117V33 (goes from 5V to 3.3 nicely).
7. For transistors buy a transistor kit from ebay (you will mainly need 3904, 3906 and 2222s. Any other transistor you will need, buy in 10 packages from mouser. I always buy 100, and I always end up with lots of leftovers - and leftovers take up space. Remember, Space is what you will run out of long before you run out of money.
8. Pots - you will need Lots, from good manufacturers. You will either reuse pots all the time in different projects, in which case you want them to last, or you will build them into a device you will use for a long time, again, they need to last. 10 turns are expensive but worth-while. Lots of 3/4 turns one (larger ones). same with trimmers, buy good quality from Mouser or Digikey.
9. Buy a bunch of dev boards, and LCD displays that fit the dev board. I bought about 10 MEGA2560 boards that get swapped around for different projects, but MSP432 will do just as well. eBay has them for cheap.
10. Battery holders for 2, 4 and 6 batteries. + 9V battery leads (or make them from old 9V Batteries)
11. Pin headers. I got about half a kilo of these at a surplus sale two years ago, and I have used up about half of that already. Buy different styles, though straight are best, and can be bent if they are long enough.
12. Solder - buy thin 60-40 in a half kilo roll. More than that, and it will get old before you are done.
13. Lots of stripboard, veroboard, prototyping board, thin pcb, single and double sided. PCB is to an EE as paper is to a painter. You need different types and lots of each.
14. Buy a good side cutter. I got a Knipex, and it has served me well.
15. If you don't already have one, buy a good drill and some carbide bits for different screw sizes!
16. A USB isolator is great. Adafruit has a 20$ one.
17. pushbutton switches. Something with nice long pins that is big enough for a "manly" finger!
18. ICs - only get them from reputable distributers:
4N35 optoisolators x 10
TL072 x 25
TL431 voltage reference x 5
LM386N (for those times you need to "hear" a signal!) x 5
Low voltage (3~5 volt) Rail to Rail OpAmps (anything you can get for cheap) x 10
Get a few microcontrollers that are through hole. ATMega328Ps are fine x 5.
Crystals: 4, 8, 10, 16 MHz crystals. 5 of each from eBay - or a few bags of crystal kits from eBay.
19. Cool Parts that you should have at least one of:
high power IR LEDs.
high Power RGB LEDs.
High Speed or High Resolution ADCs and DACs.
wide frequency range VCO e.g. MAX260X series
ARM microcontroller dev board
Precision opamp
Precision Voltage source
Digital Switch
Digital Pot
Encoder Switch
20. Anything else is really not worth while stockpiling. I have a ton of "Jellybean" parts that I will probably never use, simply because they are the lowest common denominator. Just buy a few extra whenever you need them for a specific reason. And don't forget, you should probably simulate a circuits, and reading all the datasheets and looking at similar circuits (what part have others used in this role or setting) before e.g. buying 5 different parts to test out for yourself.
Remember when making orders from Mouser, DigiKey, Farnell, etc. Don't pad out your purchase (e.g. for free shipping) with "more of the same" resistors, transistors, etc. Instead, buy a cool part that you have never used before (e.g. Hall Effect sensors, MEMS Gyros, etc. etc.) There is a lot of learning value and fun to be had in playing with more those parts.