The description says 33% of pickups become sacks, but that number is too high.

https://bindingofisaacrebirth.wiki.gg/wiki/Sack_Head

Suggested condensed format:

Some Pickups become grab bags.
Coin symbol: 10%, symbols for bomb, key, pill, rune, battery, 20%. ~15% of all chest/room clear pickups. Affects existing pickups.
Does not affect pickups spawned by grab bags or held items.

Errata lines:
T. Keeper: affects fading coins dropped by enemies.
Head of the keeper: affects coins dropped by enemies.
D20/Dinfinity/dice shard: affects rerolled pickups.
Equality trinket: doubled pickups have separate chance to become a grab bag.