As i understood it. Please someome correct me if im wrong!
You have box to fill and $10 to spend. You can go spend your $10 on new stuff at a store but you can also put some of your stash in the box also without it counting towards the $10.
OR
You can go shopping in your house and "spend" your money on items you already have.
Or some combination of both.
I am counting stuff from my stash as "free" items. Little extras to go with the stuff I bought.
Again Please If I got it wrong, please tell me! This is my first as well.