The bag of holding is an idea, of something that is more than it appears. A space, bigger on the inside, then the out.

This changed from reducing the weight of gold and allowing objects to be transported as if they were 60 pounds, to an actual extra-dimensional container.

The idea is classic, and it's interesting that you're viewing this text on a real live "bag of holding", for your tablet or computer screen always weighs the same, yet may carry hundreds of games, movies, or other items.

Delta points out that the bag of holding may be a rules hack, designed to fix an economy bug, allowing money to be transported and used in real world ways to make up for the fact that the weight and value were changed to make dungeon exploration more exciting.

It is one of the first items to receive a cursed version, a bag of devouring, designed to punish those who found a bag in the dungeon and assumed it was a bag of holding. Or more nefarious, a bag of transmuting, which functions as a bag of holding, but eventually turns gems and precious metals into worthless stones and rocks.

Modern variations and iterations continued, from the Quiver of Ehlonna, Portable Holes, and Heward's Handy Haversack, to the idea of Bagworld, put forth in Knights of the Dinner table (and Hackmaster 4th edition), postulating the entire universe of bags of holding all connected via dimensional channels. Later versions would change the portable hole to create a 5 foot depression in an object, making it a literal hole. Both the Quiver and the Haversack produce the item requested or desired by the user (in the sense that they make it available, not that they create it.)

The extra-dimensional space involved has created hundreds of internet discussions and arguments, about what would happen if you pierced a bag of holding, to the effects of storing one bag or portable hole inside another. What happens if you put a bag of holding in a lake? What happens to people in bags of holding? Food? Is what you put in your bag safe? Various rule systems and games have given their own interpretations on the issue.

Modern avant garde interpretations by the old school renaissance (Irony?) include bags of holding that are actually living maggots (via +Bryce Lynch), that store their goods inside their stomach.  Dungeon World quantifies the way a bag might not return what you wish to retrieve. Another entertaining revision of the bag, is from the 3rd edition book, Dragon Magic, Hoard Gullet, allowing you to swallow up to 100 pounds and 10 cubic feet a level and store it in a second extra-dimensional stomach for around 8 hours, with the ever present danger of vomiting the goods back up.

The idea of storing and transporting more than you can naturally carry, is one of the natural evolutions of play. It provides additional treasure capacity for high level characters in megadungeons, allowing their delves to be more successful. In other styles of campaigns, they often appear when the focus changes from small area exploration, to exploring hexes (between levels 4 and 6) and a focus on more "adventuresome" play. When the necessity of this utility was reduced by the reduction in weight of treasure and the shifting gameplay priorities of accumulating it in 3rd edition, the additional functionality of the Harversack was added.

Whatever game you're playing, it will likely have a bag of holding, and that bag of holding won't be like anyone else's bag, in anyone else's game. The answers you have to questions over the bag of holding aren't going to be the same as another's. But the classic trope of a bag of holding belongs in a fantasy game.

Top 10 ways to add unique bags of holding to your game

10) Bags are actually living creatures that must be bred and have personalities and different capacities. Those without skill at handling animals will be poorly equipped to handle such a creature.

9) All bags of holding are produced by the same wizard conglomerate and are affordable and common, there can't be a downside, right?

8) An eyeball the size of a volleyball, fully functional. An orb surrounded by flesh, with eyelids and lashes. Items are pulled out of the pupil, much to the distress and chagrin of the eye. Only functions in dim light, otherwise the pupil is too narrow to reach in.

7) A hat, that functions as a bag of holding, but will only produce an item in trade for another. Groups of coins should count as a single item for this purpose.

6) A mirror, about as sturdy as a normal mirror. The reflection shows the contents of the mirror in the background. You reach into it to retrieve items.

5) A blinding helmet, the metal covers the eyes. If put on, you see a virtual space filled with darkness. Anything you were holding can be set in this space and stored. Anything retrieved while in this space, you will still be holding when you remove the helmet.

4) A dreamcatcher of holding. Items can only be stored and recovered while sleeping.

3) A circlet of holding. A golden ring about 2 feet across. Anything dropped into it from one side is stored, reaching in allows you to retrieve items. There are no special features of things passing through the other side of the ring.

2) Orifice of holding. A spell, enchantment or magical item that causes an orifice on the person to act as a bag of holding. This could be an ear, nostril, anus, vagina, or any other opening on the persons body. The opening will distend. The distention is painful.

1) A horn of holding. The horn must be sounded in order to retrieve an item.