How about an option in the loot menu to change one material into another? Say you can’t find a battle manual but 50 trainer manuals could be converted into one battle manual in say 24hrs.
Or, say you can’t find a warm cape but 10 chainmail shirts could be converted into one? Time conversion factor and required items based on star tiers and rarity.
For simpler items: say 10 potent leaves equals 1 crypt mushroom in 3 hrs, etc.
The idea came to me when I ran out of string for arrows, “string” seriously… Here I’ve got rope and leather strips, but can’t make a string. Went out to farm and no “string” to be found…
Simplified version: Create a two star item with 10 of any other two star item, etc, etc. (Would be a nice way to help to reduce the amount of material surplus)