Beware of fast food and shun the gas station snacks. These will empty your wallet faster than you can say "I call shotgun." Instead, bring a cooler and load it up with econo-size snacks at local grocery stores along the way.
And don't forget the power of the dinner sandwich. Dining (and especially drinking) from the grocery aisles is much cheaper than eating out. For example, at $5.99 for a 9-ounce tub of turkey, $2.39 for a loaf of bread, $4.99 for sliced cheese, and $2.99 for mayo, that's $16.36 for about 11 sandwiches, or about $3 per two-sandwich dinner [source: Pricible.com]. If you like your meals hot, bring a camp stove. You can grill up hamburgers or grilled cheese sandwiches for much cheaper than if you pulled over at a diner.
That said, a little realism goes a long way. If you know you won't actually cook every meal on your road trip, plan and budget for a more realistic meal schedule. Maybe a diner meal a day will chase the culinary boredom away?