I have driven my 2006 equinox all day until about a half hour ago. I came home to pick up some paint supplies and put everything in the car and suddenly the battery is dead. NO WARNING at all.

Chances are that either one of the battery terminals is loose or corroded, or the alternator isn't charging and you "ran out of battery" If that was the case though, you should have had an indicator light on the dash. Very rare, but I have also seen a battery just flat out die with no warning. (actually happened to me once)
If I had to guess at which has happened, I'd go with the dirty terminals. 99% of the time that is the problem.