In Bhagavad-gītā (9.26) Kṛṣṇa says:

Kṛṣṇa is so kind that if anyone offers Him a leaf, a fruit, a flower or some water, He will immediately accept it. The only condition is that these things should be offered with bhakti (yo me bhaktyā prayacchati). Otherwise, if one is puffed up with false prestige, thinking, "I have so much opulence, and I am giving something to Kṛṣṇa," one's offering will not be accepted by Kṛṣṇa. The fruit vendor, although a woman belonging to the poor aborigine class, dealt with Kṛṣṇa with great affection, saying, "Kṛṣṇa, You have come to me to take some fruit in exchange for grains. All the grains have fallen, but still You may take whatever You like." Thus she filled Kṛṣṇa's palms with whatever fruits He could carry. In exchange, Kṛṣṇa filled her whole basket with jewels and gold.

From this incident one should learn that for anything offered to Kṛṣṇa with love and affection, Kṛṣṇa can reciprocate many millions of times over, both materially and spiritually. The basic principle involved is an exchange of love. Therefore Kṛṣṇa teaches in Bhagavad-gītā (9.27):

"O son of Kuntī, all that you do, all that you eat, all that you offer and give away, as well as all austerities that you may perform, should be done as an offering unto Me." With love and affection, one should try to give something to Kṛṣṇa from one's source of income. Then one's life will be successful. Kṛṣṇa is full in all opulences; He does not need anything from anyone. But if one is prepared to give something to Kṛṣṇa, that is for one's own benefit. The example given in this connection is that when one's real face is decorated, the reflection of one's face is automatically decorated. Similarly, if we try to serve Kṛṣṇa with all our opulences, we, as parts and parcels or reflections of Kṛṣṇa, will become happy in exchange. Kṛṣṇa is always happy, for He is ātmārāma, fully satisfied with His own opulence.