The Muffin Button is a button that can supposedly make blueberry muffins.
It was first mentioned by Goku in "No Country For Old Namekians" where he asked Dr. Briefs where the button was while inside the spaceship, but Dr. Briefs denies even considering creating such a device.
It was mentioned again by Goku in "Operation: Dodoria Drop" where Goku is seen holding a muffin and stated that he got it from the muffin button after being questioned by Dr. Briefs on where he got the muffin from.
Goku mentions it a third time in "Stop! Celebrate and Witness, Goku's Back From 100X Fitness!" by saying that the Muffin Button somehow gave him telepathic powers, which allowed him to read Krillin's mind.
The Muffin Button makes its first official appearance in the third and final part of "Freeza: The Final Cut" when Goku arrives at the control room in Freeza's ship and presses a button, which generates a blueberry muffin. Delighted, Goku proceeds to press the Muffin Button multiple times, generating more and more muffins until Namek exploded, seemingly killing Goku.
In "News of Future Past", it was revealed that Goku survived the explosion of planet Namek because of the Muffin Button. He explained that all of the muffins he created formed a seal around him, which protected and fed him all the way to planet Yardrat, eventually learning how to teleport from being fed by the Yardratians' sick.
The Muffin Button makes another appearance in "DragonThing Z Kai" where this time around, Goku generates so much muffins that he turned planet Namek into a giant muffin, which explodes into over several muffins.