RS Components do free delivery on all online orders which makes it economical to order only a few LEDs, resistors etc. of various values costing next to nothing for experimenting. I used to feel guilty about this and try to wait until I had a larger order, but they end up sending your order in 5 envelopes from 3 different countries anyway so don't worry about it. RS are not always the cheapest supplier but for small orders the free postage is very useful and delivery (here in Australia anyway) is quick.

If you're not sure what you need I'm sure there are several readers who could scan the online catalogue and suggest RS part numbers for you even if we don't have components we can send you directly.