Do you need someone to play a cleric? D&D without magical healing can be pretty rough. 5th edition helps out some, with the Hit Dice mechanic. Pathfinder players have learned, over the years, that Use Magic Device and a Wand of Cure Light Wounds can cover for a missing healer, once you get high enough in level to make that combo work (in terms of skill ranks and gold).
But it really shouldn't be necessary. Here are some mechanics and items GMs can add to their game to help them run without a cleric.
Save healing potions for battlefield healing, to keep them special. And let's design some mechanics for out-of-combat healing.
Do you see your game as hard-core Sword and Sorcery?
Drums of Valor (Artifact)
When a character plays these war drums loud and fast for 5 minutes, all their allies within 30' regain hit points equal to the drummer's hit dice, if the drummer is within 1 mile of a hostile creature with hit dice equal to or greater than the drummer's.
Pathfinder: Playing the drums is taxing, and requires a Perform (Drums) check, DC 10, or the drummer is Fatigued for 1 hour.
5e: Playing the drums is taxing, and requires a Constitution (Drums) check, DC 10, or the drummer gains a level of Exhaustion.
Is your campaign a low- or no-magic world?
You're going to need some sheepsgut stitches on that wound, and a poultice. And we'd better splint that ankle while we're at it.
Cost: 5gp/charge, up to 10 charges
Time to use: It takes 15 minutes to apply a Medic's Kit,
Prerequisite: Can only be used by characters with at least 1 rank in the Heal (or Medicine) skill.
Effect: Spend 1 charge from a Medic's Kit to help a character regain hit points equal to their current hit point total. Like curative magic, any hit points not needed are not used.
Example: Ragnar the Fighter has 44 hit points (maximum) but is down to 8 hit points. Ragnar spends 15 minutes and spends 1 use of the Medic's Kit. Ragnar regains 8 hit points. Ragnar now has 16 hit points. Ragnar spends another 15 minutes and another use of the Medic's Kit. Ragnar regains 16 hit points. Ragnar now has 32 hit points. Ragnar spends another 15 minutes and another use of the Medic's Kit. Ragnar gains 32 hit points, but can only gain another 12, so now Ragnar has 44 hit points - his maximum.
Design goal: This is fairly realistic. When a character is down to 1 hit point, it implies some serious injuries. It will take several uses of a Medic's Kit and possibly a few hours of medical treatment to get the character back into strong fighting shape. Because the improvement is proportional, the value of a Medic's Kit scales. But it doesn't scale perfectly. A 15th level character with 1 hit point left will need more uses of a Medic's Kit than a 2nd level character will. But a character at half hit points will always need just one use of a Medic's Kit, whether they have a maximum of 10 or 200 hit points.
Are you running a game of epic fantasy?
Great Destiny (Blessing)
When a character with a Great Destiny spends 5 minutes out of combat after defeating their opponents, they heal all hit point damage. This is something people in the game setting might notice: These characters seem to have limitless long-term reserves of energy, luck, zeal, will, and dedication.
Design goal: In epic fantasy, the PCs are usually heroes with a destiny or at least something special about them that others might notice. Robert Jordan famously lampshaded this trope with the diagetic concept of "ta'veren."
Is this a whimsical fantasy setting? Or high-magic?
Unicorn Amulet (Artifact)
When a character holds the amulet to their heart, and a specific prayer to call a unicorn is chanted repeatedly for 1 minute, a Unicorn appears before the holder and remains until its work healing the injured is done. The unicorn is willing and able to use its healing abilities on any character the amulet holder asks, but it will not fight for any reason. This amulet can be used any number of times per day. If the unicorn is attacked, it disappears and will not return when called for 1d6 days.
Pathfinder: When summoned this way, the unicorn's Cure Light Wounds spells are "at will" instead of 3/day
5e: When summoned this way, the unicorn gains an ability, "Healing Horn (at will): When the unicorn touches a character, it regains 10 hit points."
Design goal: For a whimsical or high fantasy setting, I wanted to create something that keeps healing magical, if not makes it more magical!
Is this a Fantasy Horror setting?
Characters who are trapped in a Dark Pact can recover all of their hit point and ability damage by trading something to a demon or devil in a ritual sacrifice. The ritual begins by contacting the creature. The deal is struck, and then the creature makes its demand. The character must give up what is asked immediately, if it is a material demand, or else forfeit their soul. The sacrificed item is consumed. Some sacrifices call for a mystic loss or a deed in the future. If the character does not perform the service requested within a year and a day, their soul is forfeit. To get out of the deed without losing your soul, you can always seek an Atonement (per the spell).
Characters who have not forfeited their soul roll 1d20 to see what the creature wants. Characters who have forfeited their soul already must roll 1d10+10.
1-3: Half of the food remaining from the food the character carried in the last day
4-6: All of the character's water (including wine and other beverages, but not magical liquids like potions)
7-8: The number of hit points regained, in gold pieces
9-10: A gemstone or piece of jewelry of the character's choice (worth 1 or more gold pieces)
11-12: The character must burn a dead creature (could be an animal or a monster killed in a past fight) and let its smoke reach the sky
13-14: The character must sacrifice a weapon they carried in the last hour (even a cheap dagger will do)
15: The character must speak a serious blasphemy against a god of the GM's choice
16: The character must let the creature spy on them as with Scrying for the next day
17: The character must reveal to the creature the name of a character they care deeply about - a name they have not shared with the creature until now.
18: The character must reveal to the creature a goal they have - a goal they have not shared with the creature until now.
19: The character must reveal to the creature a fear that they have - a fear they have not shared with the creature until now.
20: The character must agree to kill a criminal that the creature asks them to at a later date, within a year and a day. The victim will be someone who has committed a crime against a person (not just property)... but they may be someone the character or another PC cares about, needs for their goal, or fears will be harmed (See results 16 and especially 17-19).
How about a cool narrative mechanic?
Tell the Tale
If one or more players tells the story of their last combat encounter in a way that makes it sound exciting, without using any mechanical game terms, the party can heal all their hit point damage.
Design goal: Often the mechanics and tactics of combat make it more of a game than a story event. A mechanic that rewards players for refocusing the game on storytelling after the tactics of a fight not only lets you run without a cleric easily, but also brings the game back into story mode after a battle.
How about a neat story mechanic?
At the start of each adventure, each player writes down three things that their character cares about, that might come into play in the upcoming adventure. These are called Twists. During the adventure, they can "spend" one of their Twists to grant the whole party a full heal-up of all their hit point damage. The GM decides a result or secretly rolls 1d20. On a 11-20, nothing happens. On a 1-10, the GM must place the character's Twist in serious peril in the next encounter.
Design goal: A mechanic that gives the party a big recovery, but then puts something important at stake, lets the players control the pace of the game. If they want to have a cool, high-stakes scene show up, they can ask the GM for it using this mechanic. GMs should have no trouble placing things in peril - especially once the players have identified something to place in peril for them and done the work of convincing themselves to care about and believe it could happen all by themselves!