A new way to cheat in Nancy Drew games has been discovered! You can copy/paste save files from one game, into another game, in order to manipulate your inventory.
For example, if you load a "Danger on Deception Island" save file in "The Haunted Carousel", you get taken to the start screen, with some items already in Nancy's inventory. The same thing happens, if you load "Secret of Shadow Ranch" save files in "Danger on Deception Island".
Those two, Games 8 and 9, appear to be the only games where this trick works. I didn't experiment much with manipulating the save files of other games in the series, but Game's 8 save files don't work with Game 7, and Game 11's save files crashed Game 10. So that was as far as I tried.
As for WHICH inventory items appear when you use this glitch, I guess we'll have to do some experimenting. It seems like each item is connected to another one. Like, if you have the canteen in Shadow Ranch, that gives you the chess quiz in Deception Island.
I have no idea what this glitch would be used for. Speedrunning? It saves some time to have all the inventory items at the start of the game, but those are not games where the endgame sequence is triggered by items. So you'd probably have to play a fair amount of the game, no matter what.