If you're riding you've got to eat ... it's that simple. If the riding is a 2 hour blast around the trail centre then chances are, any eating can wait until you get back, if it's a 'proper' ride then you'll have to re-fuel at some point. One of the big problems with food can be weight, if you carry the stuff you really feel like eating then you'll possibly also end up with a big increase in the weight of what you're carrying. Compromises may be the only way!
Another consideration is the energy content of what you're carrying / eating. You might have reduced the weight of your food down to ultralite acceptable but if you've sacrificed its energy content in the process, then it may all be in vain.
I'm informed that when mountain biking, you burn 3.9 calories per pound of body weight every hour. That means that if you weigh 11 stone and are going to be riding for 8 hours, your body will use 4805 calories ... that's a lot of calories when you consider that government guidelines advise 2000 calories per day for the average adult.
There's also health issues to consider. Fat contains more calories per g than any other food type ... however, stuffing 4 blocks of lard down your throat isn't going to do you much good in the long run, although it will supply you with lots of calories. I once heard of an ultra runner who survived on nothing but pork pies throughout a rather epic run as they contained the highest number of calories per g than anything else he could carry.
Obviously the figures above are going to vary for numerous reasons. However, if you only use them as a rough guide it's still surprising how much food you might be eating and unfortunately carrying.