I'm gearing up (literally and figuratively) for a 3 day 2 night backpacking trip with my 15 year old son.  So far, we have gotten 2 backpacks, sleeping bags, sleeping mats, hammock kits, sets of trekking poles, rain wear, and one stove/fuel set-up, and water filter.  Aside from food, what other essentials do I need to make sure to get?  I plan on getting a stuff sack and was going to get trail type binoculars and a knife. Thanks!