Finally figured out the box code. Slightly guessed the last two symbols since I was not 100% certain what the corresponding items on the poster represented. Really well made for having minimal time for puzzles after finishing the art. I've made a couple escape games for jams too and they can get complicated, both with coding and creating puzzles. I can't think of any suggestions beyond add a sound track (which I know you're already doing) and if you have time, add sound effects for some items, like a click when pressing the arcade button or unlocking a lock.
Viewing post in Escape From the Basement jam comments
I agree having the scenes change is not too complicated, but setting up a working inventory like yours (outside of engines with built in ones) has always been really complicated for me. In a lot of my past escape games, I just skipped having an inventory with selectable items because creating code for it was just too complicated, though I have been working on an inventory template in GDevelop I really should try out sometime.