The first step is to find the backpack:
1. Starting from Mannshire we must go to Outpost Eestver
2. Must find the enemy fortress and kill the guards
3. There are two entries: enter the one at the right side
4. The backpack is over the table, can’t miss it.
Using The Backpack
Once we got the backpack, we can use it in two different ways:
1. We can use it directly from the inventory
With this option we don’t get extra space but we can keep the backpack and don’t lose the cape’s bonuses.
2. We can use it from the cape’s slot
With this option we increase our inventory space but lose the cape’s bonuses.
To use it, just right click over it and select “use”
Keep in Mind
Keep in mind that will have a hardder time to use things from inside the backpack (will need to open it each time) and some items you can quickly use (like bandages), can’t be used from there (must open the backpack and use them manually).
So, it is best to store not consumable items or stuff you don’t plan to use in combat.