When the weather is so wonderfully warm, like it is this time of year, I love to drink lots of cold water to stay hydrated and prevent myself from overheating.
When I know I'm going to be out for a while, walking, hiking, or on a boat, I always bring my reusable water bottle along. I love to drop ice cube sticks in the water to keep it extra cool, but in this heat, it tends to cool down really quickly.
The insulating properties of neoprene keep the contents of your bottle cold (or warm). Plus it absorbs all that annoying condensation that always drips on the outside of your bottle. It's easy to clean, lightweight, inexpensive (you can order it for $7.95), and such a great idea - definitely a must for warm weather.