I define long as over 50 miles and 20 miles as short.
Water is fine for short to medium rides. For long rides I use PowerBars and drink Accelerade. When taking Powerbars be careful. You need to counter the high sodium with water and not more sports drinks that have high amounts of sodium. I start out with two bottles of Accelerade and then switch to PowerBars when I replenish with water along the way. Everyone has their "magic formula", but just water is not going to do it over 40 miles.

During organized events there is the trusty soft pretzel.