Teabone3
commented
2 years ago 
All possible in Lua already, all 3 of them really. Here's a working example (old video much improved since then which now has item swapping and stacking etc):
https://youtu.be/bVFjiuhqp8s?t=214
My suggest for TGC if they are to implement a stock inventory system that they go about it simplistically in a way that is more versatile to all genres. It should be noted however all this is already possible in Max.
earthling45
Got a few suitable candidates for the base inventory (or inventories) to be used within Max's RPG mode, not sure how much this has been discussed internally at TGC, but regardless these are some of my (and i'd imagine most gamers) personal favorites.
Bethesda Type (Fallout/Elder Scrolls) AKA Navigation-Based Menu Type (Screenshot from Fallout 3)
Functions as an inventory but also as a navigation menu for quests, maps, stats and etc, perfectly functional and not just exclusive to Bethesda's games, though at times can be a tiny bit cumbersome to go through for first time players, players have to double click to use items, or hold down a key to set the numeric key bind for weapons (though in Max this could also work for regular items.)
Backpack Type (Screenshot from S.T.A.L.K.E.R: Anomaly)
Extremely simple, user friendliness is this systems best contribution, and it shares this in common with the third and fourth example as well, simply drag items into the corresponding slots for weapons and armor respectively, regular items (like medkits) are used or dropped within the inventory or by using keybinds, the most important part about this system is the backpack itself, as different sized backpacks can expand or minimize your inventory.
Grid System (Screenshot from Deus Ex modded with GMDX)
Similar to example 2, but also uses the classic RPG staple of the hotbar, basically drag items into the hotbar, press the corresponding numeric key to use item, though you can also use items directly from the inventory like in the second example. This system has never gone out of style and is still being used today.
Grid System with item rotation (Footage from Peripeteia demo)
The only difference with this one is that the grid allows use of items rotation within the inventory, allowing users to make room for more items, otherwise it functions the same as seen in the previous example, added simply due to my own bias of loving item rotation within grid systems.
(All of these systems also (but not always) shows different stats, such as level, weight of items/max weight, exp left to gain, how much currency you hold, etc.. i think it's important to decide whether these things become their own menus or are included within the inventory)
Felt like this was important to touch upon as there are more than one type of RPG, and thus - more than one type of inventory that you can adapt into Max, whether or not you decide to have a few different systems, or you use a hybrid or allow people to completely customize their inventory (maybe similarly to what's done within the storyboard?) i think these examples can give some ideas as to how the base inventory system could or should look like when you're ready to release the RPG mode into GameGuru Max.
P.S. I don't expect you to blatantly copy any of these systems into Max, take your time and do whatever you feel is best for the end user.