Buy stamps at the vending machine
Have already read some tips with the small change collecting and do that automatically, whenever I come home (because I can not off too thick a Portemonai!).
I then take this small change with it for a stamp (for a letter 58 cents so far) and put it in the machine in front of the post office. I save the time to queue long, because there is always a long queue at the post office with us.
And if I buy a stamp and have it not suitable, I print out the difference always (for example, 2 cents) and at some point I have enough for a Maxibrief (DIN A 4 envelope) together.
That makes sense, because you need some space to stick all self-adhesive postage stamps from the machine ... does not look nice, but who does not honor the penny ...