I was recommended to use efeberk's Scene Combine script, which seems to be the most useful choice for combining items in-menu. But how I'm supposed to combine the items when the game is running?
(I also know that the items are categorized accoirding to this part of the script)
#[[item1, :type], [item2, :type], [result, :type]],
#[[item1, :type], [item2, :type], [result, :type]],
[[1, :item],[2, :weapon], [3, :armor]],
[[8, :item],[9, :item], [3, :armor]]