If there is a long line at the cashier, while you are waiting, you may want to get your change ready (if you know the price). This will reduce the waiting time for the people behind you. This comes from the Japanese attitude of wanting to please other people or not wanting to bother others. In order to have the paying process go smoothly, it is best to have your wallet ready, instead of having to rummage through your bag for your wallet and rummaging through your wallet to get the money! Yay for efficiency!