How many songs do you put in your digital "crate?"

I usually find that I’m using songs which total at 2,5-3 times the length of my set. So for a set which would last 2,5 hours I would use approximately 7 hours worth of music. If you want to be flexible, you would still need to follow Terry’s advice and double that to 14 hours of music in your crate.

It all depends a bit on your mixing style though, especially on your tracks/hour ratio.