The only supplement I have used for biking (mountain and road) is Citomax. It is supposed to help reduce the lactic acid build up in muscles. I try to drink lots of plain water and to snack on bananas and energy bars. Fresh pineapple is also a good pick me up snack.
For me it was one water bottle of citomax and one of water. The water bottle got refilled often whenever I had an opportunity to do so and the citomax only got refilled once on a century ride. But I did carry extra premeasured packets. Which came in handy when a friend of mine cramped up badly on a century ride. I don't think we were half way through yet when he just cramped really bad and fell off his bike.
After helping him to stretch the cramp out of his leg, I gave him a packet to mix him his water, which he drank down about half way. And I gave him a spare packet to mix when he finished. He made it through without another cramp.
Just for the record, I am not endorsing this product, just saying that I have used it before.