This page of the gui allows for certain additional equipment to be added. When crafted heart containers are used, they are added to the trinket slot in the bottom right. Update 1.3.5 to Tinkers Construct included knapsacks, which can be equipped in the appropriate slot. When equipped, a new tab shows up on the gui which opens a secondary inventory within the knapsack, similar to the backpacks crafted in the Backpacks mod. It cannot be opened without going through the inventory screen, as the Backpack mod packs can when they're equipped.
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