As a cleric, I am a bit frustrated by the ratio "how many spells I know" vs "how many of them I can actually prepare each day", and end up turning my back on spells that can be really usefull but only in very specific situations.

Then, rummaging though rules just for the sake of it, I came across spell scroll-scribing. If a rituals allows me to spare a spell slot, and a scroll allows me to cast an unprepared spell, would my cleric be able to imbue scrolls with ritual spells, allowing me to cast unprepared spells without using any spell slot?

I do know that "ritual" means longer cast time and restricts spell level to the lowest, and crafting scrolls might not be worth it (regarding the cost of it), but it still seems that would be an interesting combo (as in "maybe-a-little-overpowered" interesting) and I am a bit surprised that I don't see anywhere some kind of rule preventing me to do that.

Am I wrong somewhere? Or am I indeed able to store some rituals for later, like pickles in a vinegar jar?

You can make a spell scroll of any spell, not just a ritual spell. Casting from a scroll does not use spell slots and you don't need to have the spell prepared.

If you make a scroll of a ritual spell you would use the scroll to cast using the normal casting time not the ritual casting time. This works great for Gentle Repose so you can use a scroll to cast it as an action and suspend the time limit for a spell like Revivify. That'll save you a prep slot until you get Raise Dead (which has a 10 day limit anyway, so next day prep it and rez the fallen). The diamond may cost 500 gp, but revivify and scribing has a combined cost of 550 gp so it works out cheaper. Still, either way, not a spell you need to prep.

Why the hell did I think using a scroll also used a spell slot, I wonder... Re-reading carefully with your answer, it makes more sense.

Thanks!

These items can also help:

Pearl of Power
Ring of Spell Storing
Spell Gem *
Ioun Stone of Reserve

Storing spells is a nice way of reducing castings/preps for a future day. At the end of the day, if you have the right spell slots you can store the spells you need so you can have access without needing to prep them or using slots on another day. The Pearl lets you recover a slot up to 3rd level, so it's an extra spell slot per day.

Along with wands, rods and staffs that can cast certain spells (like Necklace of Prayer Beads, Staff of Healing or Rod of Resurrection) which can help reduce the need to prep these spells.

* = Spell Gems are something I recommend because it can cast the stored spell as an action instead of the normal casting time (yay for instant Raise Dead) and anybody can cast the spell inside it without needing attunement (you only need to attune to it to put a spell into it) - so even if you go down, the lumbering fighter could take the gem from your pocket and cast the spell on you. Or, at higher levels if you have the right spell gem:  storing a Hallow spell so you could, as an action, destroy all fiends around you with ease.

Quote from Cyb3rM1nd >>

* = Spell Gems are something I recommend because it can cast the stored spell as an action instead of the normal casting time (yay for instant Raise Dead) and anybody can cast the spell inside it without needing attunement (you only need to attune to it to put a spell into it) - so even if you go down, the lumbering fighter could take the gem from your pocket and cast the spell on you. Or, at higher levels if you have the right spell gem:  storing a Hallow spell so you could, as an action, destroy all fiends around you with ease.

 
Not quite. to be able to cast from the gem, you need to know the spell or the spell needs to be on your class’s spell list. so you pretty much need to be a spellcaster yourself.

But i still really much recommend this for any spellcaster able to cast spells with long casting times. it is a pretty hard game changer if you can, for example, cast leomunds hut as an action and be invulnerable unless it's dispelled.