I'm trying to update the (awesome) Adventure Backpacks mod from version 1.7.10 to version 1.12.2.  https://www.curseforge.com/minecraft/mc-mods/adventure-backpack.  I understand that because of the version jump, everything needs re-rendering and some methods won't work the same as before, but given it's functionality as a combination of a gravestone-like system, multiple buffs to use depending on the backpacks, lava and water bucket system and mobile crafting, (and many more), I believe this mod is worth it.  The only problem is that I can't even figure out how to decompile the darn thing so I can begin troubleshooting it!  If you can't help me do it (or don't feel like it), can you please tell me if it is possible and how much effort it would take to get this done?  I'm not exactly a master when it comes to coding in java... ?

https://github.com/Ugachaga/AdventureBackpack

Ah... well...

Don't I feel silly... (^◡^") 

OR if you had some patience and don't need the fancy functionality from said mod (just the backpack system) you could just install Baubles and this mod who let you equip Shulker Boxes in the bauble's chestplate slot, and setting up a hotkey to open it like a backpack.

 

For easy access to shulker boxes (by default you need to kill shulkers on the End) you can use CraftTweaker (or a datapack when 1.13 modding is out) to add shulker shells to a loot table like junk fishing, or create (with CT too) a recipe with accessible materials for this.

But anyway just a random idea, imo more close to vanilla due to use of a existing block.

I always preferred CopyGirl's Wearable Backpacks, but there are many choices and that's a good thing.