[Diabolical Artificer]

As David says, your cap stash will grow because you often have to buy 5 caps when ordering and often buy more than needed to round your bill up. Also it doesn't matter how many caps you have, you never have the one you need.

That said if working on valve stuff, 10u 350v axial caps are in loads of circuits, like the 1k/10k/100k resistors, 47u 25v and 47u 350v also. Also grab a few 0.01u 630v axial, the yellow ones, they are used extensively as coupling caps. With transistor stuff the cap value range is a lot wider, as is the voltage range, but a few 1u, 10u, 100u, 1000u in various voltage values will come in handy. However if you get 63v rated caps, these will cover most applications, EG you can use a 63v rated part instead of a 35v one, sort of.

When buying caps, try and get those made by manufacturers with a good reputation, like Vishay, Sony, Panasonic, Rubicon etc and if you can afford it use 105 degree specked parts.

Another wrinkle is to grab any old TV's or other old stuff and take out the PCB's and unsolder the caps and any other decent parts. On the whole the poly and ceramic caps will still be ok and the electrolytics can be used for prototyping or as a stopgap substitute, once you've checked they're ok.

Andy.