As far as food, pack light. All you want is enough food to give you energy to get you through your matches. If you over-fill your stomach you'll feel sluggish, under fill it and you have no energy. That said, granola bars are always good, watermelon/cantaloupe, pineapple..I like watermelon and cantaloupe because it is saturated with water, and also has a lot of simple sugars which are good for energy with no crash. Beverages, water and gatorade G2 (the low-calorie stuff) because all you're looking for is hydration and electrolytes.
As far as prep, these days turn into long days..so without breaking a sweat, stay loose, keep moving around a bit until about half hour-45 minutes before you go on the mat and go through a warm up routine that slowly builds your heart rate up, and you just barely break a few beads of sweat before you step on the mat.
As far as on the mat..don't let the chaos of combat get into your head..keep the same level of calmness or intensity that you do in the gym..that chaos/panic factor will burn you out very fast if you let it..
Hope this helps, and good luck! Oss!
