When you calculate your part values for your circuit, you usually get values in the following ranges. If you calculate a value outside these ranges, you may have a math error.
Resistors 10 ohms to 1Mohm, we also have 10Mohm chip resistor, 1/4W leaded resistors at 1.2, 2.4, 5.6 ohms
Power resistors $.20 to $2 Make up what you need by seriesing or paralleling 20 ohm 1W at 5 cents each, and lesser quantities of 3 ohm 10W, 22 ohm 2W, 120 ohm 2W, 20 ohm 25W, 120 ohm 25W. We also have nichrome wire to make custom resistors, 4.68 ohm per foot, usable to 1 amp.
Ceramic chip caps 4.7pF to .1uF. We have about six values in this range. If Z5U dielectric, it varies maybe 20% with temp.
Electrolytic caps 10uF to 10,000uF. Good stock of 10uF SMD and 100uF leaded radial.
Caps between .1uF and 10uF are in short supply. If plastic film, costs 20 times more than ceramic. Most cap applications (but not timing circuits) can accept higher capacitance, of which we may have a good stock, .
Note about caps: series is less uF, parallel is more uF. This is opposite to resistors.
Potentiometers: have to be purchased, values tend to be 100 ohms to 1 Mohm. For audio, try to get "audio taper" or "log taper." If you buy in a store, think about getting a knob at the same time. Radio Shack's small parts are in metal cabinets, in drawers.
On-line vendors are Mouser, Digi-Key, and many others. The Mouser on-line catalog is very good but it is so extensive that it may be frustrating. Some vendors have minimum orders, be aware of that possibility. Sometimes we can get parts off of old consumer products rather than ordering new. But be careful of the dangerous picture tube in CRT TVs.