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. The noun forms of the word, meaning "a wasteful person" or "one who returns home after a period of bad behavior," relate to this biblical story. You can also use prodigal to describe something that is very abundant or generous, such as prodigal praise. Prodigal comes from the Latin word prodigere, "to drive away or waste."