Hello! You can pin consumables or other items to your hot bar from the inventory (see the keys/buttons shown at the bottom of the screen). Controls for selecting and using them are shown in the Options menu. This isn't covered yet in the help tutorials.
Gear will serve more of a functional purpose as the difficulty increases as areas are added. An auto-equip toggle is an interesting idea!
Onyx will receive new attack abilities as early as the next update! For now, use the dodge ability or slide attack to get out of corners, as they can move through enemies.