During your travels in the Lands Between in Elden Ring, you will need to use many different items to restore your Health Points or Faith Points and buff yourself and your equipped weapon, distract the enemy to sneak by undetected, and so on. With crafting being a thing, you can expect to use items in Elden Ring even more than you did in Dark Souls or Bloodborne.
Like in the Dark Souls games, you will need to equip items to the Tool Belt via the Equipment menu to use them. There are 10 Quick Slot items, so there's enough space to equip all the items you need in addition to the Sacred Flasks. To use an item, you need to select it by cycling through the equipped items with the directional buttons and then pressing the Square or X button.
Elden Ring also further expands the items that can be used on the fly with the Pouch. Thanks to this, it is possible to equip four more items that can be used by holding the Triangle or Y button and then pressing one of the four directional inputs. To equip items to these shortcuts, open the main menu, press left to highlight a Pouch slot, and then press Triangle or Y to pick the item you want to equip. With the spectral mount Torrent or spirits having to be summoned by using items, this system essentially allows you to have them ready without sacrificing any traditional item slot.