I've seen these products where they sell you falvoured straws to drink you milk with. What a waste of money.
Since I've been a kid, I have used peppermint crisp chocolates for exactly this.
You simply bite off both sides of the chocolate exposing the peppermint, then you put the chocolate into your glass of milk and start sipping away.
This is a lot better, because not just does it make your milk minty flavoured, you also get to eat the straw afterwords.
Go ahead an try it for yourself. It is quite a tasty snack.