They also stay in assigned positions: if you have health potions under the '2' key and consume them, then, after obtaining another one, it will immediately go to the right place. Potions in the belt do not share space with the equipment. These slots contain additional rows (visible when you hover the cursor over it), which will expand as you get better belts. You can put mana regeneration or health potions in there. Even if you do not initially intend to change the skills, it is worth assigning a fast travel portal key to flee the battlefield in a critical situation. You will still need to click LMB/RMB to use the skill.

Below you will find information about useful keyboard shortcuts that will speed up and facilitate the gameplay: