Pumping at Work - Use This Milk or Frozen?

Mom32712

I have a small freezer stash - about 100 oz. - and will be going back to work next week.  For daycare, should I send each day the frozen breast milk or what I pump at the work the previous day?  Just thinking that I should use oldest first.  I started a freezer stash because I heard I should but not really sure what I should be using it for.....