so to start the fire it burns 2 fuel items?
Well 1st off you can read my reply on a similar topic (checking to see if an item is one you want) https://forums.unrealengine.com/showthread.php?104329-Food-replicating-feeding-Trough&p=494563&viewfull=1#post494563
However it all depends on how you want to implement it, Currently I think ARK burns fuel from weakest to strongest (Thatch, Wood, Sparkpowder,??)
if you want to go for that route, you will have to create a PrimalItem var that holds the “most eligible” fuel item to consume.
So as you cycle through the inventory (you can probably see the foreachloop in my post linked above) you compare the item (from the inventory) and check the var (isValid) if the var is empty (as the 1st round it is) check to see the inventory item is a fuel item, if the var is populated (round 2 and up) you will have to check to see if is what I found before a better fuel source or worse and do you assignment there.
if you happen to only have 1 stack in the inventory you might have to default to consuming from it as there is no other stacks. Because the quick a dirty way is to just say consume item from inventory index of  (which in code means slot 2 as indexes start at 0 in the code world) but you still run into the issue of 1 item inventories.
Depending if you want the quick and dirty is inventory array length > 1 consume index  or  (I’m pretty sure you can’t access the light fire command if there is no fuel) but you run into “Is it really a fuel item in the second slot?” so to make your logic/code do what you want you can cheap out and just say fk it, or you can create your “business rule” then the acceptance criteria and then the plan of attack
“When the torch is lit (start trigger) I want it to consume 2 fuel(?) items”
If there is more than one stack, it will take split the consumption between two stacks
If there is only one stack check to make sure that its quantity is greater than one so there is 1 used to start the fire, and the remainder is for the extra consumption
(Unless if there is just 1 stack you don’t want it to light the fire at all)
Plan of Attack (more or less plan out what you need to complete this coding wise)