Master Weaver

Sunny could simply trap a bit of space within the backpack, making it much larger on the inside than it was on the outside. Of course, that would create several problems of its own, which he would then need to solve. 

For example, there was the issue of weight — a simple Memory like that would be able to contain many items, but it would also weigh accordingly. Having a spatial storage Memory was of little use if its master could not lift it, after all. Luckily, Sunny had long mastered enchantments that manipulated weight. By adding a simplified version of the [Feather of Truth], he would be able to give the backpack the ability to reduce the weight of all items stored inside.