Boiled eggs, and jerky (particularly if you can make your own) or simply cooked meat (like browned ground beef). Since you will be expending gazillion calories, dried fruits and nuts are going to be just fine. Fresh veggies keep as well as fruit, btw and just as easy to take along. When we go on a day trip, I pack a huge container with leftover cooked meats, boiled eggs, cheese and lotsa veggies. Cold fried ground beef is amazingly good, actually.