What do you pack for a 14-20 days european tour?

My wife and I are planning to go on a trip to Europe in Mid August this year. We would like to travel light and at the same time have enough clothes to wear in the places we intend to go. POLAND / AUSTRIA / FRANCE / SWITZERLAND / GERMANY / CZECH REPUBLIC. Any suggestions? Can anyone recommend good and not so pricey places to board in these countries? Any other valuable suggestions to make the trip memorable?