Don't ruin your trip by stressing over money -- or running out of it. That means a little work on the front end. Know how much your lodging costs, as well as admission fees for attractions you plan to see. Use Internet mapping sites to calculate your driving distance, then determine your approximate gas bill (add an extra tank or two for getting lost or choosing to deviate from your planned route). Don't forget to include the cost of any tollways you know you'll pass through.
Food costs can be a little trickier to figure. Decide ahead of time which meals you'll be eating in restaurants, then set price limits. Or give yourself a total daily food budget.
Finally, throw in a little extra money for emergencies, souvenirs and stumbling upon some can't-be-missed sights.