On business trips, your travel expenses are 100% deductible and your food expenses can be deducted at 50% of the total. Keep all of your receipts because even things like dry cleaning and tips are considered a necessary expense when you're out pounding the pavement in new markets.
Your local day-to-day mileage incurred for business purposes can be written off as well, so give the same attention to tracking your mileage on smaller trips that you would to the expenses of an overnight trip. For many people, the mileage deduction is the more realistic deduction than first class tickets to New York. Remember, you have to be able to justify any trip and preferably show the payoff to your business resulting from it.