The 30min rule devised by an unknown author can be used to train the willpower.The waiting period puts you in control of your will.

Are you hungry? Wait 30min before eating
Are you thirsty? Drink in 30min
Are you tired and you want to go to sleep?Go for a 30min long walk. Are you angry? Wait 30min before you express it.

This can help you overcome the urge for instant gratification.