When playing with Pikachu/Eevee, they will sometimes give you a gift with an item in it. Some of them that I have received contain Stardust/Heart Scales, but I have also gotten some new items that I have no idea what to do with, such as the Stretchy Spring/Marble. Do these items serve any purpose at all?
The only use found by people so far is selling them for a small amount of money. Don't believe it has any other use other than its cute your Pokemon have it to you.