My players are exploring ancient ruins. This will be an ongoing thing where they find the entrance, leave while some NPCs do some excavation, and return to find more ruins uncovered. Rinse/repeat for the foreseeable future.

I don't like the ideal of "magic paper that never disintegrates"  for scrolls, so the players will find small engraved runestones that are functionally scrolls. I'm also open to other ideas if anyone has any.

I also don't like the idea of potions (in glass containers) that just last for ever. I'm struggling to come up with a functional replacement for potions that are not liquid in a bottle. Any ideas would be most welcome.

Thank You

Really any consumable item can stand in for a potion or scroll. It could be a bit of bone carved with a prayer of healing or a small ornamental gem with a protective elemental rune etched on it. It could be a small stick doll wrapped in snake skin bindings or a petrified scarab shell bearing the symbol of some lost deity. It could be as wonderous as a bit of unmelting ice that casts a faint glow of power or as common as a dingy bit of rusted coin stained with blood. The only thing that really matters is that the act of releasing the power within destroys the token or trinket. 

Speaking of trinkets, any item from a trinket table could, in theory, stand in for a consumable item in a pinch. 

Logic and Magic don't often mix well. In my mind when an item is created that becomes magical, that allows it to have a superior lifespan and potency!

I've also felt like "scrolls" are an unlikely item to find in a dungeon after being abandoned to the elements, and "but they're magic" has always felt like a cop-out to me.  I know it sounds ridiculous, conjured fireballs and lightning bolts are fine, but durable scrolls are where I draw the line, apparently... just a personal thing I guess.

In my campaign I've re-skinned some scrolls as "bottled spells" -- not exactly potions, but the stored essence of a spell in a small glass vial.  For example, a vial containing a swirling cloud of shadow casts a Darkness spell when the vial is opened, or a vial of dust that levitates an object or creature that it's poured on.  As long as the glass vial is intact, it seems more "believable" to me that the essence of a spell would withstand the ravages of time.  Of course, your party will need to make some decent Arcana rolls or use Identify to know exactly what they're looking at, unless the vials are labeled.

In addition to the stone and bone mentioned, I’ll add in fossilized wood — though how it fossilized in a dungeon is beyond me. 
For potions you could do small edible crystals. Like magical Advils. Or have some strange plants or mushrooms growing there, and eating one gives a potion effect. And once they harvest one, it just doesn’t grow back. 

Keep in mind that “scrolls” could really be anything including clay or stone tablets. IRL archeologists find ancient tablets all the time. Sometimes they break, but as long as they haven’t been mishandled and there’s been little geological activity in the area they might last for thousands of years. Plus the whole “magic” thing could explain why they haven’t too.

And depending on the environment even parchment or papyrus scrolls can last for centuries. Parchment isn’t really paper at all, it’s sheep skin that has been scraped smooth enough to write on, and can be scraped clean again with a knife and written upon again. (Hence part of why there’s the small knife in the scholar's pack.) Parchment is very durable. And papyrus is almost a woven cloth made of plant fibers and glue. Not as nice as paper, but could possibly survive, again depending on the environment. As long as it’s a dry, arid environment parchment and papyrus could survive, hence how the Dead Sea Scrolls lasted as long as they did. If it’s a good environment for mummies (deserts, frozen tundras, peat bogs, etc), then it’s probably good enough for scrolls.

As for potions, if they’re digging underground then there could be all kinds of molds and other fungi, mineral deposits or chemical soups galore down there that could have all kinds of effects on people. And then there’s possibly also secretions from heretofore undiscovered subterranean amphibians that could work too. Who knows what all might evolve in such environments?

One more point about scrolls; they are often stored in containers to help with the preservation over time. I know game modules tend to just state that they party finds a "scroll of" but doesn't mean it has to be rolled up parchment lying on an cold damp dungeon floor.  The item can be in an airtight case which is wrapped in leathers and stored in a water tight chest. 

But clay tablets, copper medallions, or a box containing a menagerie of stone carvings can all be use for consumable spell production.  Other inspiration for you can reimagine for homebrew items: Necklace of Fireballs or Robe of Useful Items.  You can also have the spell inlaid on shield or bracer that vanishes once the player reads it (your call if it reappears at dawn). 

For potions, have the party find small sealed containers with mixed groundings and powders inside.  Instead of drinking they smear the contents across their chest or face and the magical power is present until the magical dust fades off or the player chooses to clean themselves.  Alternatively, you can use a player skilled in Arcana to add water and other digestible liquids to with the power to create the potion with failed attempt resulting in hilarious side effects.  And if you don't like the concept of drinking; then have the characters make perfumes and ointments out of the grounded ingredients. 

One other thing to help, list some of the mundane items that the NPCs will find during the excavation.  Then reimagine how some of these items can converted into a consumable magical item. 

leather (especially tanned)lasts a llllooooonnnnggggg time. howsabout spells tattooed on tanned leather?

as for potions, just magic hardtack. it lasts FOREVER

There are lots of things that could be consumables.   Fruit makes for a nice thing - it takes a long time for trees to grow and you can easily control how long it takes to get a single Healing Orange.

Then there are clay tablets - what people did before paper, after all. Read it just like a scroll, if not quite as convenient to carry.

Incense sticks also can work.  Light to activate them.

Asian fantasy often has 'formations', which I was never clear what they were.  I think they are supposed to be several flags you plant in the ground in a formation.

I read a book where 'writing' was done by little beads on a string (that is - the book I read was just letters, but the people in the book 'read' beads, like braille). So a book would be a big reel of this string, with beads of various shapes having the function of letters. I read another book where a wizard used a grammophone (record player) to record spell casting, and set it up as a trap. Of course, in the latter case, the 'scroll' was reusable, which isn't intended here =)

The Mayans used special ropes, tied in intricate ways, as a stand in for writing.  It was not exactly characters, but functioned as a memory aid.  

Maybe some potions can be crystalized. Magical rock candy.

Although still technically “liquid in a bottle” a mechanical alternative to potions are what I call “vials”. 

The potion is drunk by the player to apply a buff, whereas the vial is thrown at enemies, exploding and splashing to apply a debuff to them.  They can be used by anyone, but usually give martials decent options beyond “I swing my sword”. 

An example could be some thing like a vial of despair, which explodes in a 15 ft radius when thrown, causing all targets who fail a charism save to freeze in panic, missing their next turn and knocking their initiative count to 1. 

If you don't want your potions to survive centuries in liquid form, make them dehydrated. The party just needs to add water (or wine, or holy water for a healing potion... however complicated you want to make it) to the powder to reconstitute the potion