Some kind of audio signal generator. There are kits, there are plans, maybe even some on eBay. You don't need something that goes way up in frequency - 40 kHz is more than enough. Twenty kHz is probably adequate.
Simpson 260 is the classic V-O-M analog meter and I have a couple. Triplet makes a similar model but I don't remember the part number. In any event, these 260's are all over eBay. I like analog meters when I want to see things change. Like the voltage of a car battery when I crank the starter. Or the voltage drop between the battery and the line input to the starter. Things where a DMM will still be converting long after the event is over. If you are buying used, look for the model with the mirrored scale - it helps eliminate parallax errors when trying to get precision results.
I like analog scopes and I have a Tek 485 that I bought off eBay for a couple of hundred bucks. I've had it about 12 years and it still works well. HOWEVER... I bought a Rigol DS1054Z and it will be my most used scope primarily for the features. If I need to look at signals over 50 MHz or so, I will use the 485. Hack the thing (directions elsewhere) and get 100 MHz of bandwidth and serial decoding all in a $400 scope. More than adequate for most hobby needs. Four channels is great for those of us dealing with digital buses. Not so terribly important for audio work. Still, who knows where this hobby goes...
Any DMM will probably work - I bought a couple of EEVBlog badged DMMs just to support the cause and because the branding is cool. These are fairly expensive meters but they will last a lifetime. I gave one to my grandson. I also have one of the very expensive Flukes (because I could) and a Vichy impersonation (still a very nice meter) but the EEVBlog meter is on my bench. I also bought a half dozen of the cheap Harbor Freight meters. I'm not sure what to think of them but I gave my grandson 3 of them to do a science fair project demonstrating Ohm's law. He won... Guess the judges liked knobs and readouts...
http://www.eevblog.com/store/I just bought a Hakko FX880D, also for my grandson, and it looked like a really nice unit. I saw one of his projects and the soldering was excellent. Personally, I have a Hakko 936 but they are out of production.
For cutters and pliers, I bought a set from Xcelite - they are pricey but they are exactly the right tools for the job. You can probably guess where they went...
https://www.amazon.com/gp/product/B000IU2KRS/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1I think a magnifying visor is critical. I'm getting old:
https://www.amazon.com/gp/product/B000BPWPRK/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1You may, or may not, want to increase the magnification with a lens change. The problem is that the focal length changes. I have another visor with the higher magnification but I'll let you guess where it wound up.
The list could be longer but this should give you something to think about.