Ever wonder what to do with flat, warm, leftover beer? Give your garden a good drink. The natural yeast in beer can help with plant growth. Simply pour the beer into a watering can and add water. Pour the mixture near the base of plants, and when you're done, cultivate the soil a little bit. You can also fill an empty tuna tin with leftover beer to keep slugs away from your garden; they'll crawl in for a drink and drown, unable to get out.