This chesed, covenantal act of lovingkindness, is to be done before the reading of the Megillah so that the poor may use these gifts for their Purim meal. The blessing is a way of asking for and receiving G-d's permission to take and enjoy that which belongs to Him.
Wine is a symbol of joy and celebration.
But it often happens that when people are 'full' and the need is gone, so is the remembrance of their source. And thou say in thine heart, My power and the might of mine hand hath gotten me this wealth. Blessed be He, our G-d, of whose food we have eaten and from whose goodness we live. You give food to all flesh, for Your loving kindness is everlasting. For You nourish and sustain all, You do good to all, and prepare food for all Your creatures that You created.