Ask HN: What is good swag in Hackathons?

As I go more and more in hackathons, I see very often bas swag, stuff that I will never use after, or completely useless. Sponsors are throwing their money. I'm organizing a hackathon in the next weeks , I wonder if HN knows some specific swag that are good for developers. (not the classic "stress ball" or "branded pen", you see what I mean)that I could share with my sponsors to provide the best for hackers that will attend. Any ideas?