Bag of Holding

Bag of Holding is a magical which has a capacity of 20 item slots to store any type of item in it. The bag has a fixed weight 5 lbs, the weight of the items put into it doesn't influence the weight. This item can be obtained in the Spellhold maze and another one can be bought from Arcana Archives affter completing the subquest: Lazarus' Spellbook. This item appears in Baldur's Gate II.

In-game description
"As with other magical bags, this one appears to be a common cloth sack of about 2 feet by 4 feet size. The bag of holding opens into a nondimensional space, and its inside is larger than its outside dimensions. Regardless of what is put into this item, the bag always weighs a fixed amount."