Actually, I was able to stack potions, and food. The problem is, if it has different values, one will be overwritten (say you have one that gives +50, and one +20, only one value will be used for both when stacked) and secondly, it simply doesn't work
. You select by default the entire stack, couldn't pick just one. Can't remember what happened when I tried to eat the stack, or how I did it, but well, it doesn't work.