When we perform a random act of kindness the 'good feeling' effect will endure for hours after the event happened.
Try helping a stranger in a small way or take the time to listen to someone in need. Perhaps donate time instead of just sending money to a cause you truly believe in. The positive feelings stemming from the altruistic act will last for a long time after the event happened. You will be giving but you also will receive something much greater in the way of happiness, purpose and the ability to step outside of your own needs.
A giving mentality in life is the right thing from a moral perspective. From a much more practical point of view, it has a phenomenal impact on our psychological well-being and can be a core driver of our success in life.
