Players usually have to face a awkward situation that there are a lot of items which are needed to carry with during playing RPG, but the backpack space or storage space is not enough. That really troubles players. That situation will not happen in Final Fantasy 16 because the inventory system of Final Fantasy 16 only allows players to carry a small number of potions and items. Fortunately, there are some methods to expand the space of storage, though it will expand only a bit. Anyway, it still can be a little helpful.

The first chance to expand players' inventory occurs in the side-quest "Weird Science". Players can receive the side-quest from an NPC named Owain in the Hideaway. It is important to notice that players need to complete the main quest "Out of the Shadow" first in order to obtain the  optional side-quest. To find Owain, players should meet an NPC named Mid to gain access to Mid's Dungeon which is the location of Owain.

When players speak to Owain, he will require players to get some bomb ash for his invention and the side- quest "Weird Science" begins. Bomb ash can be obtain by killing a Bomb King which is in The Crock in Sanbreque. After players defeat the Bomb King, three bomb ashes will be gained. When players give the three bomb ashes to Owain, he will expand the players' inventories. And then players are able to hold Potion x6, High Potion x4, Stoneskin Tonic x3, and Strength Tonic x3.

Players can expand their storage space by completing Owain's side-quest "Even Weirder Science" for the second time. The side-quest can be received after completing the main quest "Across the Narrow". And the side- quest will require players to find three spherical echoes. Players can see three green spots on the map, which is the locations of three different ruins where players can find three spherical echoes. When players get the spherical echoes and return to Owain, he will upgrade players' inventories to enable players carry Potion x8, High Potion x5, Stoneskin Tonic x4, and Strength Tonic.