Serious fitness fanatics often train for several hours at a time -- whether it's going on long runs or spending large chunks of time in the weight room. That means they probably need more than one bottle of water during a workout. A water bottle with a built-in filter that lets them refill with clean, pure water on the go is a must-have. Be sure to get one that isn't plastic, such as the Ecoflo Stainless Steel Water Filter Bottle. You can get one here for $32.99 in blue or red.