I just bought some bug out bags or go bags for a relative. My relative was overwhelmed with buying one. If all else fails with unprepared relatives, you can always help them prepare.
Picking out equipment made me more aware that my blog readers may share some of the same problems with my relative. I hate leaving people unprepared if I can post on it to help, so here goes.
First, I am assuming that you want a backpack for your bug out bag or go bag. There are three main types of backpacks. There are the frameless. Those are the ones you see most often in the department stores. They are soft all over and their rigidity depends on what they have in them.
There are two kinds of backpacks with frames. One of these is the internal frame backpack and the other is the external or rigid frame backpack.
Some of the internal frame backpacks have hard frames and some have softer frames that will form to your body or load.
External frame backpacks mostly have a lightweight metal frame, usually aluminum. The cloth part of the backpack is attached to the metal frame. There are various types of suspension systems to prevent the metal frame from touching your body.
If the metal frame touched your body with a heavy load in it and you walked a long way, you could end up with an injury. I prefer the suspension system that includes a sturdy belt in the waist area that places a lot of the weight of the backpack on the hips of the person carrying it.
It is best to have a fastening at the waist that is quick and easy to open. I don't want to spend time here going into the specific reasons for this, but it is best for your safety. Parachute buckles are good for this purpose.
It is common for exterior frame backpacks to include another strap across the chest area. I am sorry if it is not already clear to you that the waist strap and the chest strap are meant to go in front of the backpack wearer, between the shoulder straps.
There should be plenty of padding for the waist strap and hips if these areas bear much weight. This is even more so for the shoulder straps. The padding on the shoulder straps is very important.
The chest strap is not usually padded. It functions more to keep the shoulder straps from slipping out of place, than in a weight-bearing capacity.
Some backpacks are also padded where they touch your back. This applies more to frameless backpacks. Some internal frame backpacks are also padded in these areas. I have seen a few rigid frames with padding like this as well.
Rigid frame backpacks often have a system of canvas and lacings to suspend the metal frame and prevent it from touching the person carrying it. These vary a great deal in complexity and effectiveness. I almost bought one that probably required a PHd to adjust it. I can't help but feel that it is a good idea to understand how the thing works before you leave the store.
Knowledgeable and considerate store owners selling backpacks often have sandbags or other weights that you can place in one of their backpacks to try them out with a load in them. If they don't have this, I think it is a good idea to bring your own. You can walk around in the store to test it.
Make sure the backpack is comfortable and balanced for you. Make sure that you are stable when you walk with it fully loaded. Some types of backpacks work better with a certain type of physique and not another. You can only tell this by testing it.
You need to check for rubbing that might cause sores and whether you can adjust to prevent this. One thing that I watch for is the set of the shoulder straps. I am smaller than average and have narrower shoulders too. This means many backpacks have straps that will continually slide off my shoulders. This will be exhausting on a long walk.
Pay careful attention to how the various backpacks interact with your particular body type. It is helpful to have an experienced backpacker help you choose and fit your backpack. Ultimately, you are the only one who can say which backpack is most comfortable and works best for you.