Thank you to grace from 400 independent bathrooms (<3) for helping me with this list; check out d4 bags worse than bag of holding over there.
1. Hallowed Vessel: This handheld plastic bucket, printed to resemble a turnip carved to resemble a face, automatically casts Turn Halloween with a mischievous giggle when its holder is attacked by a Halloween-type monster. It consumes approximately a big handful's worth of candy to do so, and will not deign to act unless it contains candy to consume in this way. 8 slots, and it'll grumble unhappily if you put anything other than candy or toys in it.
Hallowed Vessels printed or painted to resemble specific Halloween monsters will Turn Halloweens of that type without requiring payment.
2. Bag of Sharing: The contents of this 18 slot backpack are shared with a specific, random other Bag of Sharing somewhere in the world. You have access to all of its contents, and may freely withdraw or deposit anything within the bag, every other day; when it isn't your turn, your counterparts may do the same, and your bag cannot be opened. Cutting it open in this state simply renders your copy empty and inert and theirs into a normal bag. Abusing your bag will probably disincentivize your counterparts from placing anything nice in there, though it's certainly possible they might try and game it too.
3. BaazR™ Subscription Bag: Using your BaazR™ Subscription Bag is Easy! Simply place any items you like within the Subscription Bag's 8 slots, then provide it with your billing information. Thereafter, anytime you deplete or otherwise lose any of those items, you'll find them conveniently replenished within your BaazR™ Subscription Bag. (You will be automatically billed the approximate market price of any item replenished in this manner.)
If, by some unimaginable calamity, you should ever be regrettably compelled to cancel one of your BaazR™ subscriptions, simply return the item you wish to stop receiving convenient instant refills on to the location from which you purchased it. Then, mail proof of your returns to the peak of any mountain before next sundown. You will receive a confirmation letter via conjured dove within 1d6 business days. Should you provide your assent to this letter and burn it over a fire containing the bones of an animal you've personally killed, your BaazR™ subscription will be cancelled in a further 1d6 business days, whereupon you will stop receiving the convenient instant refills we have so graciously provided you until you turned your back on us, you harlot. But we are known for our mercy and our grace as well as for having served customers throughout Laurentia for 23 years. The day wisdom finds you, the day you finally realize that you have always needed us, we'll let you back into the fold without complaint; we're here for you. All we'll need when that day comes -- and it will come -- is your credit card information, the three digits on the back, and the expiration month and year.
This process must be repeated for each item you wish to cancel your refills for.
4. The Mailman's Flail: A 14 slot canvas messenger bag sturdy enough to be swung around by the strap as a medium blunt melee weapon. Upon a successful attack using this weapon against a creature to which a number of postage stamps equal to or greater than its hit dice have been applied, declare a valid mailing address. The creature will be instantly spirited to the front door (or closest approximation thereof) at the spoken address. The stamps must have been purchased or acquired from a recognized postal authority. In most dangerous circumstances, it takes 2 action points to apply a postage stamp.
