Day Pack
While on the trail at Philmont you will find many opportunities for side hikes. Many campers think that they need a separate backpack for their day pack. The truth is, anytime that you have an opportunity to take a day pack camp will be setup. You will have your tents, bear bags, dining fly, and almost all of your gear setup. This will leave your full sized backpack empty except for a couple of things like your clothes and flashlight. Truth is you can just take your empty backpack as your day pack and not have to worry about any extra weight.
If you don’t want to do this, look at the top part of your pack. In Gregory, Kelty, and Osprey backpacks they have detachable “brains” that turn into fanny packs. They also have an extra belt buckle in case your waist buckle breaks.
If you insist on bringing a separate day pack, here are a few light weight options: