Generosity is intimately linked with happiness.
It is often said that the more generous person can be, the happier they will become. Jesus is the prime example of that belief lived out to the fullest extent possible. He gave himself for us and was the happiest person, not in a superficial way, but filled with a joy no one could take from him.
St. Francis of Assisi is another example of someone who gave everything he possessed to the poor and was filled with a happiness that endured.
Here is a prayer commonly attributed to St. Ignatius of Loyola for a more generous spirit.
Eternal Word, only begotten Son of God,Teach me true generosity.Teach me to serve you as you deserve.To give without counting the cost,To fight heedless of wounds,To labor without seeking rest,To sacrifice myself without thought of any rewardSave the knowledge that I have done your will.Amen.