what to knit with glow in the dark yarn?

I bought these four skeins of yarn a while ago - 3 of them glow in the dark, and I bought the black one to make a good contrast. But I've no idea what to make with them. I want to make or design something practical and functional, not just decorative. I'm totally brainfarting. It's one of those yarn purchases that I 'had to have', without any rhyme or reason, and it's not something that I normally do... I'm just clueless.