Some suggestions for further components:
I usually have a variety of potentiometers at hand, because you'll never have the right resistors at hand 
For simple experiments, learn how to combine capacitors and resistors in series and paralel. This will keep you playing while you get the components.
Here is an example:
http://www.aikenamps.com/AddingComponents.htm
A regulable voltage regulator, like the LM317 is also nice to have when you need to play with different voltages.
My 2 cents.