Inventory tetris(item rearrangement) occurs when player has insufficient inventory space and items are arranged sub-optimally.
This occurs because items can take different number of inventory spaces or have an unusual shape (e.g. |_ ) that isn't rectangular.
1.Much larger inventory by default(multiple pages/levels).
2.Allow stacking/unstacking items of all types.
3.Reduce visual size of items while in inventory to 1x1(least realistic).
4.Allow "bags of holding" 1x1 items that access secondary inventories that store more items by placing them in a "bag".(item portals). Most realistic.
5.Allow unlimited access to stash/storage from any place, so player has additional inventories to access besides the current.(combines with #1)
6.Allow players to create/hide/move storage containers in-world, such that can be hidden or buried for later use.(e.g. "bag of holding" hidden in a tree).
7.Allows players to place items into NPC storage.(e.g. give items to NPC that can store them safely). i.e. nearby NPC that items can be offloaded to.
8.Simply remove the expiration of items on the ground(usually done to reduce junk), allowing items to exist on the ground indefinitely.*This works best in instanced or low-population maps, that reduce chance of theft.
9.Allows unlimited transfers of items from anywhere to other characters owned by the player.
10.Replace the inventory with more abstract that scales to unlimited items(or specific numeric limit independent of visual size)