I recently took a long hike, although not as long as you are planning (mine was 2-1/2 hours through hilly terrain). I ate a big breakfast first -- bacon, omelet, the whole works. That really gave me energy all day. I didn't get tired or hungry while hiking.

I think nuts are a good idea -- they have both fat and protein.

I remember years ago (back when I weighed well under 200 pounds), going on an arduous five day back-packing trip with a friend who brought along all sorts of high carb goodies (trail mix, chocolate, etc.). Despite the number of calories we must have burned on that trip, I actually gained weight. Even when hiking, we don't need all those carbs.