Luna has a problem. She's spent all of her royal allowance, and she wants to go shopping! What's a mare to do? Ask her older sister of course! But when she is shot down for her own idea, Celestia decides that if Luna's going to get some extra bits, she's gotta earn it.

And so, Luna's going to have to clean out a vault filled to the brim with a thousand years worth of tributary gifts. Gifts she didn't ask for, or know she had, or even want! What will she do? Well, when you need bits, you do as the ponies do. Roll up your figurative sleeves and get to work!

(Based on a dream I had. Yeah, I'm a strange one.)