Single cup coffee brewing machines like Keurig have become common fixtures in homes, offices and hotels all over the world. The biggest environmental culprits of these machines are the disposable plastic cups -- otherwise known as K-Cups -- that you use once and throw away. To save money and cut back on the environmental waste, you can actually reuse them. Simply peel back the foil cover on the K-Cup and dump the coffee grounds inside into your compost bin. Rinse and dry it. Then scoop in ground coffee and secure a reusable cap -- search "Kaps for K-Cups" on Amazon.com -- that lets you reuse your plastic cups until it's time to throw them away.