Water.

When I started riding longer distances I didn't carry water. There were enough convenience stores that I was able to sustain a ride without carrying water. Now I know better. Water is a critical to performance and health. In the Washington, DC area we have hot, humid summers with some periods of time where the air quality is poor for days. There were times I went on rides and couldn't figure out why I was so tired or pooped out so completely. I now realize that I should have been hydrating better. I watch the color/frequency of my urine. That is my indicator. When it's darker I know I need to drink more. When it doesn't come out at all I know I'm dehydrated. I haven't been a huge fan of sports drinks and gel, but I'm coming around. If I have sweated a lot then I usually get a sports drink like Gatorade. Another test of dehydration is pinching a flap of skin. The more it stays pinched after release the more dehyrated you are. The skin should resume it's former shape immediately under good hyration.

I carry water on my rides that are longer than 20 miles especially in the summer months. I've gone from plastic bottles to thermal plastic to stainless steel. The steel bottles hold NO tastes, so I can put any type liquids in the bottle without aftertaste. I love the new stainless steel. I've gotten the 20 oz. from Walmart and Backcountry.com for as little as $6 per. You have to keep in mind the type of top you want. I don't drink with the top on. I tend to stop and remove the top. If you want to drink while riding get the kind of top you want when you buy the bottle. The tops are expensive when bought separately. Water bottles are a little difficult to clean, but nothing compared to Camelbak systems. I found the Camelbak systems difficult to get used to.