A Water Bottle
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Yes, you'll be sitting by a giant body of water. However, last time we checked, drinking sea water wasn't an option. Wherever you may end up, the water may be really salty (in more ways than one), so we recommend a filtered water bottle like the Brita Bottle from Brita. The bottle has a filter built in, so you won't have to keep buying bottles water. Instead, fill up the bottle directly from the tap, and the bottle's built-in filter will take care of the rest.