Use the adjective prodigal to describe someone who spends too much money, or something very wasteful. Your prodigal spending on fancy coffee drinks might leave you with no money to buy lunch.
Prodigal usually applies to the spending of money. In the Bible, the Prodigal Son leaves home and wastes all his money. You could also use this word to describe something that is very abundant or generous in quantity, such as prodigal praise. Prodigal comes from the Latin word prodigere, "to drive away or waste," combining the prefix prod-, or "forth" and agere, "to drive."