On Castle Town, if u get an apple and move it to a different slot than the default (idk if a lot of people do it but I like to put them in the last slot) and get another apple, it’ll stack with the first one.
On Spaceship, tho, if u get a potion, move it to a diff slot, and get another one, the second one doesn’t stack and just goes to the 4th (?) slot instead. I’m not sure if it’s a bug or not. My suggestion is that the spaceship potions should stack too even if u move the first one to a diff slot than the default. This is my first suggestion; hope I did it right haha