Consider using a tarp or bivy sack instead of a tent. Use almonds or almond butter for snacks. They have more calories per pound than Snickers bars. Trim your rain gear. No rain pants, or if there's minimal risk of hypothermia no rain gear at all. No extra clothes that you don't need. Use water added toilet paper instead of camp wipes. You can use each one 4 times. Once to clean your body, once to clean your bowl once to blow your nose and once to clean your butt. Hope that helps more than "start with the big 3"