The Ender Pouch is a small bag that has a player-sized inventory. (Note: If you are playing on a public server, your items may be accessible to someone else.) This is like the Alchemy Bag in that it has multiple colors with a different inventory in each color.
Depending on the server's settings, the Ender Pouch may have an inventory twice that size, or merely nine spaces large.
For the most convenience, use both the Ender Pouch and Alchemy Bag. To know why, read the section entitled "Ender Pouch v.s. Alchemy Bag" below.
To set the color of the Ender Pouch you first need a correctly colored Ender Chest and then have the pouch in your hand and shift+right click on the Ender Chest.
Ender Pouch vs. Alchemy Bag
StatsThe Alchemy Bag has 104 slots, while the Ender Pouch only has 27.
Their functions are the same, with the exception that the Alchemy Bag is player specific, while the Ender Pouch is server-specific and has more possible color codes than the Alchemy Bag. Alchemy Bags also have the ability to allow certain EE items to work when placed in them, unlike when these items are placed in an Ender Pouch.
Ender Pouch's Solution for Infinite Inventory
The Ender Pouch coupled with an Ender Chest and Buildcraft Pipes can be used to make a player's inventory infinite. Make sure that both the Ender Pouch and Ender Chest are crafted using the same colour wool, or else they won't connect. When you place items in an Ender Pouch, the items are also placed in the linked Ender Chest. By connecting a pipe system to the linked ender chest that will pump items from that ender chest to a different chest, will make the ender pouch never fill up, because every item the pipe system pumps out of the linked ender chest disappears from the ender pouch.
This infinite inventory solution is useful if you are mass mining blocks--ore, stone, dirt, sand, etc.--and don't care whether or not you keep them in your inventory.
Alchemy Bag's Solution for Infinite Inventory
Equivalent Exchange (EE for short) achieves infinite inventory by placing an alchemy bag into a different colored alchemy bag. This allows for many hundreds of stacks, but not truly infinite.
This infinite inventory solution is useful when you want to keep items in your inventory where ever you go.
Further, there are items that will automatically vacuum items into a specific bag, to avoid inventory management, and others that automatically morph stacks of lower tier items into the same EE value of higher tier items, making them truly infinite.
Use both the Ender Pouch and the Alchemy Bag.
Use Alchemy Bag's solution for infinite inventory for storing items that you need in your inventory while away/at your base.
Use Ender Pouch's solution for infinite inventory for storing items that you don't need in your inventory while away/at your base.