God is so graceful that whatever one asks for He gives them for sure. Kubeera, though he did a lot of sins in his life, due to a little bit of Shiva dharma he did, he became the deva of wealth. Puraanaas praise Lord Shiva as the giver of boons without any reservations to anybody who praises Him.
We go to Him with a big list of requests. A lot of us pray the God only when we are in some trouble. No doubt God gives the best what we deserve without questions, but aren't we doing some mistake that way ?
Let us assume a person gets a chance to go to Kalpa Vruksham and ask for a boon. If he is wise enough he will ask for the Kalpa Vruksham itself rather than asking it some other material. Once it has become his belonging he can ask anything from that. God the greatest, graceful Kalpa Vrukasha, Kaama dheenu one can think of. So is it wise to ask that Kaama dheenu some silly thing than asking the all fulfilling God Himself for us. If God be for us, for what reason should we suffer in life ? Like the drop of water that is dropped in the ocean becomes the ocean itself, we in the presence of our Lord are invaluable.
The best boon we can ask to the Lord is His liking. Finally all our actions should be aimed at satisfaction of the Supreme. Whenever a puuja or prayer is done it is started with "Shri Parameeshwara priithyartham". Only that could be the ultimate goal of any prayer. He being our divine mother and father knows what all we want and will take care of us in the best way. Doesn't the mother know the needs of the infant even before it cries ?
In fact we may not be knowing our own needs, which God will take care of for a person who surrendered himself to the Lord. In Mahaa Bhaaratha before the battle KrushNa asks Saha dheeva what boon he wants, Saha dheeva being a man of good knowledge of Shasthraas could have asked just for protection. But he said "we 'five' Pandavaas shouldn't be killed in the battle". Result ! In the battle he had to repent when he lost his eldest brother KarNa whom he didn't know to be his brother.
God became the mother and gave milk to the orphan pigs, blessed the child Thiru Nyaana Sambandhar even though they didn't ask for it. Let all the actions be done just for His satisfaction and it is His duty to take care of us