As Memphis said try and eat clean. Make sure your not eating packaged meats as they can have all sorts of crap added to them, try and stick with meats that are cut directly from the bone, that way you know they haven't been tampered with.

I normally eat some complex carbs before a training session like pasta and brown rice, I find this gives my body enough fuel to get through a workout without dying. I also eat alot of Tuna fish wrapped in a tortia for a quick snack (Canned tuna in oil, the salted cans are not that good for you) this gives me some protein to repair the damage done after my workout.

For normal meals I always have steamed vegetables accompanied with some meat, stir fry's are one of my favourites. If you are going to eat stir fry make sure you use olive oil or some other low fat oil, you dont want to cover your food in rubbish.

Lastly I try to stay away from sugar and caffine, I'm always checking those nutritional vaules on foods while I'm shopping. Sugar is empty calories and does no favours for your body, I have seen orange squash labeled "Pure Juice" when infact it has about 30g of sugar added to it.

Take a look at this link to read more about nutrition for boxers:

http://www.ringside.com/articles/nutritionforboxers.htm