If you want to keep the Santa sack, save and quit after you've delivered all the presents without returning it to Jingle. You won't get the wreath but you'll keep the bag. It'll just be an item you hold after Toy Day. Nothing can actually be put inside it.
If you want the wreath too, you'll have to do this with an alt.
Interesting, I might do that.
EDIT
On the other hand, why would I even do that. It's not like I'll be using any part of the Santa outfit ever again