Infinite money glitch. you need to click outside of the money and the coin hole to exit the machine, then quickly pick up a coin and place it in the hole, after that when you click the machine again it will have the coin's value inside but you still have the coin. you can use it as is and get a free item every time, note that you can't get that coin that is inside if you exit, so it can only be used as a free coin, so just use a 500. it's the fastest way to get all foods up to 500. But not healthy foods, I noticed that the healthy foods you get with 500, is just enough to keep you fed for the time it takes to do the bug, if you want to go the healthy transformations, then just go with 50 seeds packs. (or a thousand if you have the money, but in my experience, just using all your money up to 50 coins, getting seeds is the best way.)
by the way I noticed in the comments that not that many people know that when you get an item the vending machine says the coins you need to put for a guaranteed same item, for example 333 yen is a bottled fetus. maybe a reference to please don't touch anything? idk. edit: not all of them have a price for a guaranteed droop.