I have been working on understanding how the game decides what items go in which boxes. Obviously this depends on what place the player is at the time of breaking the box though. One thing I've discovered so far was that all items in a race are determined at the beginning of each race. So on lap one of a race, the item that will be in the last box on the last lap is already set and will not change. I haven't been able to figure out whether these are sets of items that are used multiple times or if each box is randomly generated at the beginning. I have found other small bits of interesting information such as a theory that it's also possible to manipulate the AI to not use items. I have a recording that shows this but still need to do more testing. I just wanted to let everyone know what I've found so far so they can possibly build off of it.

Wow, that's awesome. There has not been too much testing of this game in general... personally, I've always been too lazy. So it's nice to see people dedicated enough, like yourself, who analyze stuff like this.

Anyway, back on topic: Although I've never directly tested this, for the longest time I've had this theory that the game has a certain amount of RNG patterns. There are some RNG events (ghosts, pans) that seem to occur rather often and sometimes almost feel certain. For example, one Pan inside the tunnel on BS usually leading to another Pan right when you exit the tunnel and other not as specific occurences like getting significantly more pans in the final sector of NH, or plenty of ghosts in the final corners of SM or NL.

I have been somewhat unsure about this as I've never checked if these outcomes were indeed linked to other events, but it would correspond with your theory. If there actually was a limited amount of "patterns" AND if additionally we could find a way to manipulate the AI... that would be pretty amazing.