Sack Head

Effects

Coins have a 10% chance to be replaced with Grab Bags. Bombs, Keys, Cards, Runes, and Lil' Batteries have a 20% chance.
- This includes pickups spawned by most sources: room rewards, chests, slot machines, special shopkeepers, etc.
- Golden Coins can reappear as a sack when collected.
- (Added in Repentance) Coins bombed out of a Donation Machine can become sacks.
- The exception to this are pickups spawned by Isaac himself directly, e.g. with the likes of IV Bag or Fanny Pack, and contents of other sacks.
Spawns a sack upon pickup.

The item does not replace hearts, pills and chests.
The item can also replace Troll Bombs and Megatroll Bombs that are not used as attacks, i.e. generated as room rewards, chest contents and such.
The pickup replacement is applied retroactively when the item is collected: any appropriate pickup already existing on the current level may be replaced by a sack.
(Removed in Afterbirth †) Sacks on each floor tend to have the same contents, which can be taken advantage of if cards are involved.
(Added in Repentance) Picking up a Golden Penny may spawn a sack instead of another Golden Penny.
(Added in Repentance)(Cracked Key) Cracked Key in the Ascent can be replaced by a sack, thus it is not recommended to take the item if you're going to unlock a tainted character.

(Added in Afterbirth †)(Equality!) Equality!: Sacks may drop new sacks while Equality! is active, potentially resulting in massive amounts of resources from a single sack.
Head of the Keeper: Coins spawned from hitting enemies have a chance to become sacks.