You'll need healing items too, but know they can cause you to become thirsty faster. Bring food, water and a sleeping bag (if you can spare the weight) along with weapons. There are different stages to each, and they'll affect your stats and AP the more your situation deteriorates. Famine, dehydration and exhaustion can cost you in the field, so make sure you have the right items in your pockets. Enemies are much harder and aren't the only thing you'll be worrying about.
