First approach i had:
1(front and back)> armor&cap
3a/b)> armor bracelet
But at this point i was sad. Really sad.
1front)> light source with on/off switch, Oortian technology: immagine something cool like Iron-man but obviously Oortish style. Effects: during nights you can be easily spotted from the distance (i see a light dot moving around...). Switching On/Off can also be used as Morse Code or any kind of signals. Another use of this can be an interaction between light (and light color) and buildings... for example a dungeon where there are lifts that can be activated only if you have a certain color of light and so on (you may need more colors in a certain order, or a certain "power" of the light source and bla bla bla, wild fantasy takes the mic).
1back)> I would NOT add backpack. It's ugly. It's orible. I don't need more slots in the inventory. My backpack is conceptual and resides in the world of ideas. Of course i have things with me, it's just manifest so I don't need it to be showed. You will surely have a "base", a place where you have your treasure/material chests, and going around hunting with a 80 slots backpack is just something "comfortable" (and that can be placed between the items that you can buy ingame with real money, like a +10slot inventory for 10€).
But as i imagine this game: before going out of home, knowing that you can die everywhere/anytime, you will have to do a good selection of items: hunting? ok, weapons, potions, light for night-time, etc... Dungeon? Building? Exploring? Limitations on the backpack means you have to think and prepare your own set of things for what you wanna do.
So, what i would put on that slot?
This is my reasoning: when you wear the bow, you also equip arrows on it, some people already spoke about the quiver. What i propose is something "neutral": something that can be charged with arrows for the bow, but also with rope for the hook, if the light will be something that consumes a colored gleam to make a specific colored light, this 'Oortian tech quiver' is your "any kind of ammo storer"... if you make a flame thrower... well no, don't make it xD
What happen to the things i put in here? they are effectively in a different place from the backpack, so instead of adding slots to your conceptual backpack, it gives you a free space (arrows will always be there and will never occupy a backpack slot, if you put a different color gleam, the old one will go back to the inventory -or just vanish- rope for hook... all this things).
I hope that the concept is clear enough
2a)> it's the right hand, but i don't want to call it this way (there are left-handed people), i will call it "main hand" ( i'm sure you have already heard it this way... ). Precisely it's not the hand. We are talking about the Main-hand-forearm. ok? be carefull: PLACE THE MAP THERE. Instead of having a fixed space of the screen where you have a little map, put it on the main hand forearm! i will still see it roughly and when i really need it "M" hotkey will do the rest
2b)> Simple: the hook. I would take the hook away from the slot-bar, cause if i want to hit a flyng/hooked thing, it simplyy can't be something like: select hook, throw the hook and jump with spacebar while mouse-scrolling to select the weapon. and if you need to jump from a tree to another while fighting?
Put the hook on the secondary hand forearm and we will use it qith a simple middle mouse button.
3a)> That one is harder. Ready? Potion injecter. The last jewel of Oortian tech.
I immagine a sort of anklet with a needle. You put the healing potions there (as for the 1back)>concept) you will get a backpack slot free, a hotkey bindable for this item will consume a "healing charge" from the anklet. But if you want to give potion to someone else, you can't get back the potions that you've stored in the anklet.
3b)> Adaptor slot. What do I mean with Adaptor?
It gives you the chance to enhance something very specific:
craft your own -examples> swing enhancer when hooked (as you know in this moment when you are hooked and the hook is selected you can swing more than if you are hooked and with a block in your hand).
Or you want to be more agile when you build? craft your own block placement/destruction range enhancer.
you want to be a better fighter? enhance your health regen or attack speed or critical hit (if there will be crit chance) or def/armor etc...
to make it shorter: enhance one and only one specific attribute/aspect of your build, to adapt it better to your gameplay style.