You live in a dystopian future where paper and writing utensils are banned, and the world government has outlawed all dissent. How would you secretly communicate with your fellow revolutionaries?
This implies that all electronic communications are insecure.
There are several registered cases of coded verbal languages emerging to enable elements of specific groups to communicate between each other without risk of being understood by outside parties.
Jamaican patoá is easy to identify as an example. The grammatical structure and speech speed creates a barrier for outsiders. Add a very plastic use of words and you have a very hard to follow "code".
In the 60/70's, in Greece, a private language emerged between gay men to enable those people, often persecuted, to communicate. It steadilly disappeared as social acceptance rose.
The cockney rimed slang is thought to have arised out of the need of the house staff to be able to freely speak between themselves in front of the employers with no concern from reprimands.
Briar. It was designed just for this. All traffic routes through Tor, it can also send messages using wifi, data, or bluetooth. There are no central servers to hack, seize, or takedown. Pretty much the entire internet would need to be killed off.
As for face-to-face communications - that's been done for centuries to fight the good fight. No reason that can't continue.
This doesn't speak directly to your question, but in the appendix of the Neal Stevenson book, Cryptonomicron, there are instructions on how to use a deck of cards (technically 2) as a one time pad for encrypting and decrypting messages. This could serve as the foundation for secret messaging using other media than paper.
Gratuitous acts of memery. Cats, Pikachu faces, swole doge and Cheems - you name it. Arcane to the uninitiated, ever so meaningful to the inner circle.
I remember a meme years ago that described how the type, color, number, and arrangement of flowers in a bouquet could be used to convey complex messages. I'll have to scroll through my hoard, but I'll post it if I find it.
But, honestly, as long as there exists a code that is shared between dissenters, and ways to represent discrete elements of that code, communication itself is easy. You could encode anything in a medium that can represent a binary state, like lining up shiny pebbles on your windowsill: two close to each other for a binary 1, or a single one for binary 0. Or you could represent messages by how you hang your laundry to dry. Or embed it into how you play a musical instrument. You could hang Christmas ornaments in your window and use any obvious property to represent a message. You could use a rudimentary radio transmitter to send messages through radio noise. The options are limitless.
The difficult part is maintaining operational security. The limitations presented by human mental capabilities means that a very simple pre-shared secret must be used, which may be leaked or deduced. You have to know where to look, how to decode or decrypt the message, how to respond, and how to do all of that covertly. Prisoners have successfully used hand motions while cleaning their cell window to convey messages outside, apparently for years before authorities caught on.
Flower language is great because it is not universal. What a flower mean in your language and country doesn't mean the same in my language and country. And neither of it is made of words !
You can also learn hobo code. Engrave/mark signs in secret places. All you need is a sharp edged rock, a piece of chalk, or even a stick of charcoal.
Banning writing instruments is not realistic unless you’re keeping the entire population indoors in an immaculately clean prison or mental hospital type environment.
Return to Bronze Age, exchange clay tablets with secret messages in cuneiform. I can fashion a wedge-shaped stylus out of any old stick
Edit: better yet, if we don't fire the tablets, we can destroy them quickly and easily whenever we need to or just recycle them. This was common for a lot of cuneiform tablets in ancient Mesopotamia, and much of what we have found in archaeology is stuff that was unintentionally fired because the building it was in burned down
An underground movement forms that uses interpretive dance as a means of steganographic communication. The code is kept secret for plausible deniability. A parallel would be Capoeira, a combat technique developed by Afro-Brazilian slaves and disguised as a form of dance.
Food wrappers made wholly or partially of paper are banned?
Is cardboard packaging banned? Does cardboard count as paper?
Are paper sticker labels for shipping banned?
Are paper/sticker labels on all kinds of products not packaged in cardboard banned?
... I am curious as to your answer, but I struggle to concieve of a society where everything is done on electronic devices, but somehow also all kinds of paper and paper based products common to many households and vital to the supply chain and logistics that produces and distirbutes the electronic products are also banned, entirely.
Even if the answer is somehow yes, all kinds of paper based products are banned and replaced with metal or plastic or glass or something...
Clay tablets. Whittle a stick into something that can make impressions on it, bake the tablet, or really any kind of pottery.
Use a knife to etch writing into pieces of thin plastic, or wood.
Use a laser engraver to engrave glass or metal.
Make crude ink or liquids capable of staining on your own from raw ingredients, write on thin fabrics, white fabrics like cheap t shirts or certain kinds of gauze or bandaging, again with a whittled stick, a chopstick, a feather, etc.
You didn't say paint is banned. Spray paint stuff. Make stencils out of thin plastic or metal.
Glue toothpicks to thin plastic.
For any of these methods, you can make up your own language or pictogram / hobo sign style system of symbols to convey whole concepts.
And for most of these methods, the object with the writing or the writing itself on it can be destoryed by fire, immersion in water or pulverization, for more resilient material use a dremel or radial sander/grinder to obliterate the message.
This is how early Christians identified each other during the Roman Empire. They would draw the symbol of a fish in the dirt and erase it before guards and spies could see.
Nah, fancy fountain pens are way too much of a status symbol to be outlawed. I'd just write with a montblanc - there's no way those filthy proles would be able to afford something like that, thus our interests as the capitalist ruling class are preserved!