If you're at a hotel and didn't bring your own food, shame on you. You should not take the chance with unknown food prior to a race. If you're still learning then:
3 hours prior to the start time (even if you have to wake up to eat. another reason to bring your own food) consume 400 calories (low fat, low fiber). Do what Cynikal said about prep but extend your warm up time to 30 minutes and ride the course as many times as possible so you'll know where to go fast or slow and you have plenty of time to practice off camber turns and such. Practice your mounts and dismounts. They're critical to CX success. If you're riding a 40 minute race, a HoneyStinger at the line 15 minutes prior for the immediate burst of energy you'll need at the beginning of the race. If you're racing beyond 40 minutes, a regular gel right before the start so it enters your system at around 20 minutes into the race.
Drink a little make sure stuff is washed down. Unless given permission by course officials, you may not be able to feed during the race. Besides, you shouldn't have bottle cages on your CX racer anyway.
Good luck and make sure you have a whey protein source ready for consumption in the first 15 minutes after the race. Even though you're finished and it's time to drink beer, you HAVE to start thinking about recovery nutrition right away.