You can chew alot, and make sure that the food is hot. This will help the digestion so that it doesn't take as much energy from you.You know when you've had nothing to eat for several hours, then you eat something then crash? (I mean crash as in lose your energy, not hit something.) What's the biology behind that? Why would you get it *after* you eat something?
About the chewing: The best possible is to chew until the food tastes like sugar. I don't do that though, I like al dente and are prepared to suffer tiredness to achieve it