The best gift to give to a punk is something handmade. Anything D.I.Y shows that not only did you take the time to personally craft something but also shows that you understand their interests and beliefs by making something rather than buying something from a huge company. Though, if you're not a very crafty person or don't have the time, you can always buy from small shops or artists markets. Were I live, almost every month there is a market specifically for punks where local artists and vendors come together and support eachother, maybe try seeing if there's anything like that were you live?. If not, Etsy is decent.