When Cthulhu eats your sanity, you're in trouble. But when he eats your dice, he'll give them back.
The Cthulhu Dice Bag is soft plush, with far more eyes, tentacles, and wings than any ordinary dice bag. He'll hold dozens of ordinary six-siders or non-Euclidean polyhedrons in his zippered pouch. Or, of course, Sanity tokens from Cthulhu Dice. Or cursed jewels, or gravel, or bus tokens, or all of them together. Just remember that to get them out, you have to put your hand inside Cthulhu. If you are okay with that, this is the perfect dice bag for you.
Using the Cthulhu Dice Bag in summoning rituals is not recommended, but mostly because summoning Cthulhu is really a bad idea. Just let him hold your dice.