Maintain your weight instead of trying to lose. Eat brunch, a snack and dinner (instead of 3 meals + snacks). For brunch, have oatmeal or eggs. For a snack, have a yogurt and granola bar. For dinner, stick to chicken or fish and salads. Even if you can't exercise, at least you won't gain!
Cut yourself some slack, it is supposed to be fun! No need to spend the whole time feeling guilty. Decide in advance what to eat. Don't weigh yourself until you have been home a week. That way you will be back in your routine and any temporary weight gain will already be gone.