Carry three to four Power Bars (or Cliff Bars), and a large Gatorade, and large water container (the largest that will fit in your two bottle cages). If your bike fits a third bottle cage, carry a second sport drink.

This will accomplish what I find to be the most difficult part of riding more than a couple hours: staying nourished. You need to keep your caloric reserves up. Alternate: One hour, eat a power bar. Next hour, drink a gatorade. On the hours where you're not drinking a gatorade, drink a water bottle instead. You'll run out of fluids, so bring some cash to buy more during a rest stop. One bottle per hour is about what I need on a warm day for longer rides.

Yesterday I rode 70 miles (114km) with this strategy. Worked out great.