This is very difficult to do without a turbo button. Because Toad is the fastest at picking things up, you have a better chance of doing this with him, but it should work with anyone. Get a potion and throw it on top of whatever you want stuck to your head (vegetables, POWs, turtle shells, other potions, etc.). Go through the door. Now that you're in sub-space, stand somewhere with nothing to grab underneath you. Push the B button repeatedly as fast as you can. If done right, when you come out of sub-space, you'll grab the item under the door so fast that the game doesn't seem to recognize it. The item will be on your head and your hands will not be holding it there. You can keep playing as usual, picking things up and such, but now when you go through a door, or climb a vine to the next screen, the item will be in your hands ready for you to throw.
Submitted by: Brett Notter