S'well Vacuum Insulated Stainless Steel Water Bottle, $35.79, available at Amazon (price varies by color)
This one's a given. A reusable water bottle will prevent you from buying plastic bottles or using plastic cups. And, while "water" sure is in the name, you can use these vessels to hold pretty much any liquid, so long as you're willing to clean it.
There's no need to go fancy here: If you're down with toting a glass mason jar around or still have your Nalgene bottle from summer camp, those both make great options. If you're in search of an upgrade, however, there are plenty of options that manage to be hip, cute and stylish, even though we're still talking about a water bottle.
S'well bottles are among the more popular brands on the market. They're beloved for their sleek design, their ability to keep drinks hot or cold, and their condensation-free exterior.