I decided to make a mod that I personally would actually use, and I notice myself using backpacks, satchels, etc quite a lot, so I made a backpack heavily inspired by Akali's back satchel from League of Legends (no I don't play it).

It has HDT, but it's only on the small charm on the back. The bag itself is rigid and unmoving.

How to Obtain:
It's a clothing item exclusively found by crafting it. It requires no perks and has no skill requirement, and has a craftable enchanted and non-enchanted version. The enchantment is a fortify carry-weight enchantment at 100 power.

Requirements:
-HDT SMP: I've added HDT SMP physics to the small charm, so this mod requires HDT SMP. I've noticed that if you don't have it installed, the charm simply disappears from the outfit - Usually I'd expect a crash, but I couldn't make the game crash with this mod.
-BodySlide and Outfit Studio: On the recommendation of SunJeong, I've given the mod sliders to adjust the forward/backward and upwards/downwards position, as well as scale for those who require that sort of adjustment, be it because of a custom race or clipping.
-Version independent. As far as I can tell, there shouldn't be anything about this mod that requires a specific version of skyrim, so it should work in 1.5.97 and 1.6+. I exclusively personally tested this in 1.5.97, so if you have any issues in 1.6+ let me know and I can further test and release a patch.

Conflicts:
SOS uses slot 52 as well, so this mod won't function very well with that. I've had users tell me that slot 47 occasionally works.

This mod uses slot 52 on the body. I've had a friend test it for me and they found that, in their heavily modded playlist (1000+ mods I believe) that equipping this item on males unequipped vanilla armours. I'm not sure what mod they have that adjusts \n
those armours, but to avoid this situation all you need to worry about is that this mod exclusively takes up slot 52, so any mod using that slot will not be usable with it, unless you edit the records in CK/xEdit.

On using xEdit: I didn't test any other slots, but it should work fine on any extra/unused slot in skyrim, there's no strict requirement for this being slot 52, that's just what I ended up using.

Technical Specifications:
The item is a slot 52 clothing piece with 5 weight, and comes with two crafting recipes. It has 0 armour value.

Due to my personal laziness and not wanting to UV-unwrap this again, this mod uses three different textures. The main one is 2k, with the other two being 512x512. The model itself is also roughly 13k tris, mostly from a desire to reach a certain level of quality over performance.

Relative to other mods on the nexus, this one shouldn't be too hard-hitting on performance. If you have performance issues with it, it may be related to HDT rather than the textures or mesh, but I have no way of testing low-spec performance with the mod unfortunately.

Credits:
-League of Legends; Specifically the Akali character's new design as inspiration for the model
-SunJeong for the massive amount of help in both recommendations, assisting me on Outfit Studio, and helping me understand some basic concepts surrounding HDT SMP that I wasn't aware of
-Terrance for helping test the mod in a highly-modded playlist

I'd also like to mention:
-Teemo.gg for references - I used their 3d model viewer for Akali
-Pulcharmsolis for the outfits in certain screenshots taken (Armors of the Velothi Pt.II)
-Blender as my primary 3D modelling program
-Adobe Substance Painter as my texturing program - Pre-packaged materials from SP were used
-Nifskope as my .nif model implementation program
-GIMP and Paint.net as my texture implementation programs
-Creation Kit as my asset implementation program
-BodySlide and Outfit Studio for outfit implementation and adding sliders to the outfit
-Skyrim as the game I've implemented this object for