Why is it only possible to stack some equpment and not all (that are the same)
you can stack upgrades (amour, shoe, helmet etc.)
but you can not stack "Books" and couple of other things...
beside this bug.. then I could suggest that you are able to stack equitment that are the same... so if you have 3 artworks they are stacked... if you have 2 identical amours the are stacked (but they need to be identical)
the setup that are now, with the 4 titles on 4 row are a little outdated, and should be renewed.
maybe a sub menu with "all" "equiptment" "bonus"
you might also start adding an minimum lvl for the hero the be able to handle the equiptment... so low level heros can handle low lvl stuff and higher lvl stuff you need to gain some experience before (this way you can earn even more money (even that I hate myself saying this)
you could as well add one or more parameters to the hero Attributes: Experience (to push for faster experience that will work like cp, added each day), (health recovery, be able to add faster recovery, and not only through equipment)
with more attributes it makes the first stage of the game even more fun with the hero... as only 2 parametres are quite simple to manage.