1) 250 to 300 calories per hour while you are riding on rides over 2 hours.
2) Look up HealthStatus.com and others for the number of calories you might be burning on a tour.. You may want to eat that much or less.
3) Look up your route on a map and see where the shops along the way might be. Carry enough so you can consume 250-300 calories per hour between those shops. Buy groceries for the night toward the end of the day.
4) This evening, go to your local grocery store ... the biggest one you've got. Wander the aisles. There's a lot more food in there than just Clif Bars!!