We can not pack everything into our Osprey Atmos 65l ahead of time because we don't know how the food will be distributed, we don't know how much cookware we are going to carry, nor do we have the tent that we have to carry. This is for a Philmont 14 day backpacking trip with BSA. If we don't have room for the sleeping pad nor tent inside the pack, how do you suggest that the tent and sleeping pad be carried on the outside of the Osprey Atmos AG 65l backpack? I think that the tent would go into the compression straps at the bottom of the backpack. Where should the sleeping pad be attached and what kind of straps should be used? On a separate note, I heard that each scout needs to be prepare to carry around 45lbs.
If it were me, my tent and pad would be two items I'd want to ensure are inside my bag simply to protect them. A hole or tear in either one from getting it caught or dropping the pack onto a sharp rock could ruin the trip. That said, if your pad is foam and not inflatable, I wouldn't worry about it as much. I see a lot of people attaching their pads to either the top or bottom of their packs.
But if it just isn't an option to get them inside, the Atmos 65 has two straps at the bottom covering the sleeping bag compartment and you could just use those to attach the tent. Depending on which tent you have, I would check the compression sack it comes with. If it's thin, I might upgrade to a thicker one just to add protection for the tent. Additionally, see if you use the side straps on the pack to hold the tent poles vertically as this will offer them greater protection as well.
Enjoy the trip - a couple of my friends and their sons have done Philmont with BSA and loved it
I havn't used an Osprey Atmos 65 and I agree with @Dad_Aint_Hip about ideally keeping my tent inside the pack but needs must.
I assume you are using a closed cell foam pad rather than an inflatable. If so I would use the sleeping bag compartment straps to attach that. If the provided straps are not long enough you can buy generic straps from most outdoor stores. You may need to temporarily strap it vertically to reduce the width when travelling to the trailhead.
For the tent I would try using the side pockets and compression straps. Put the poles up one side and the rolled tent up the other. This may not work if your tent is too big and it does reduce you options for carrying water bottles...should still work on the tent pole side... but you might want to add some bottle pockets to your shoulder straps.
Depending on the packed tent size and shape you can used the pack's lid. Generally "brain" type lids adusts on all four "corners" and you can trap gear between it and the pack. This may only work if the pack is fairly full...seems like that is not your problem.
However you choose to strap on the extra gear, make sure to test your rain cover if you expect wet weather. Waterproofing internal gear with a compactor bag is an inexpensive technique that can make a rain cover optional unless excessive rain is possible so something to consider.
I have an Atmos 65 and an REI Passage 2 tent (not a small tent). I can usually fit the tent horizontally inside my pack if I put the poles on the outside. I've got one of the long folding foam pads that I strap on the bottom outside the sleeping bag compartment. If I'm tenting, I just undo the divider between the top section and sleeping bag compartment so I have one big space (if hammocking, I leave it connected and my tarp goes in there).
Will you be carrying 14 days of food?
I am not sure exactly how the food is being handled. Since the sleeping pad is inflatable, I can not strap it to the outside of the backpack. I am going to undo the divider now since the Kelty 550 down sleeping bag does not compress down small enough when it is in the stuff sack.
If you must strap your tent or sleeping bag to the outside of your pack, I suggest wrapping a small tarp around them to protect them usally a couple wraps works fine and will keep safe from rain and punctures.
Are you saying that your down ag will not fit inside its included stuff sack? That seems odd. Try really mashing down on the bag.
I would think the folks at Philmont could give you information on the size of the tent, the cookware, and the weight and space required for grub. They have run these trips before.
Ditch the inflatable for a closed cell foam mattress. Much more foolproof.
I expect you will be sharing the tent with someone else which means you should be able to have one of you carry the poles and stakes and the other the tent body. If that's the case, the poles and stakes will easily attach to the side of your pack using a water bottle pocket and side straps. The tent body can then be folded in any configuration needed to get it into the pack. Even if you end up with the entire tent to carry, you can split it so that the poles are outside and the body inside.
As for the sleeping bag, you don't need to put a plastic bag in your backpack which makes it harder to pack. Once you have your sleeping bag stuffed, just put the stuffed bag inside the plastic bag and wrap that up or get a water proof compression bag. Sea-to-Summit makes them and REI sells them.
As for stuffing your down sleeping bag, I'm assuming you are using a compression bag? If not, try one out, even if its not the waterproof type. They really help with getting the size of a down bag down to a manageable size.