For a two hour strenuous mtb ride, I go with two gels (Power Bar brand), about 6 dates and a little less than two liters of water with Gookinaid Hydralyte to 50% recommended concentration. That covers the fast burning carb and electrolyte needs very well. In July and August, I'll increase to fluid to nearly three liters.
I gave up on energy bars. The fat content inhibits rapid absorption of the carbs, but they do handle the hunger issue on longer rides. The dates do that fairly well. On longer rides, I may carry a jelly sandwhich with whole grain bread as back-up (plus another gel with a few more dates).