At it's heart, Walkabout is a game of cultural appropriation.
There it is, I said it.
It's name is an appropriation of an Australian Aboriginal term. (If you are from outside Australia, don't give me any crap about using the term Aboriginal vs Aborigine vs Indigenous vs Koori, universities have been debating this for decades and are still arguing over it. Different members of the cultural groups descended from various pre-European tribes and nations prefer different terms of address, and many of them are simply happy that they are being referred to at all in a context that doesn't involves deaths in custody under an inherently tainted colonial legal system).
The characters in Walkabout portray neo-shamans in a post apocalyptic watseland, drawing their inherent spirituality from the myths of the Australian Aboriginal people. They appropriate this system of spiritual belief because it seems to fit their new world better than many of the religions of the past.
When 99.99% of the world's population have died, the vast majority of religious structures have fallen. 99.99% of the priests are dead, 99.99% of the wealthy are dead, 99.99% of the atheists are dead. The survivors are all appropriators of various cultures from the past.
The rich members of the new world see the pre-apocalyptic world through the lens of the surviving media...how accurate would your interpretation of the modern worlds be if the most comprehensive source of information was data files from Fox news?
The poor scavengers read the few books that weren't burnt to keep people alive and warm during the nuclear/volcanic-ash winter. The vast majority of information in the decades leading up to the apocalypse had been digitised, so the great electromagnetic pulses left the scavengers with tabloid magazines that had glossy hard-to-burn pages, religious books in sacred holy buildings. But with 99.99% of the teachers dead, reading becomes a hard skill to acquire, everyday survival is more important. History returns to word of mouth and becomes distorted through iterations of a new oral tradition (a tradition that as to be rebuilt from scratch).
Every culture in the world of Walkabout is a pastiche of cultures, subcultures and ethnic heritages. Skin colour doesn't mean a whole lot when 99.99% of the other people matching your "race" are dead. For humanity to survive, any mate would be taken, a fertile mate regardless of the race would be desired. Those who couldn't bring themselves to "cross-racial" procreation found their lineages at a dead end.
In a world with no races, a world where cultures are forged by the adoption of stereotypes and fragments from the past, everyone appropriates. Long distance communication is sporadic at best, even over a few hundred kilometres. When you take this in consideration with the fragmentary knowledge of the past, people have no idea what to expect from the rest of the world. There will certainly be some erratic common beliefs in the new nation states of the Australian continent...perhaps they will believe that Samurai defended the great wall against the Mongols, perhaps they will tell tales about Gaulish heroes valiantly fighting against Vikings, Roman legions and Nazis, maybe they'll recall the way Union generals fought against the Aztecs at the Alamo. That was a forgotten time, a time of myth and legend. When someone tries to call them out, they might ask for proof (and since no-one has proof from that time it might end up getting settled by a drinking match or a brawl.
Every character in Walkabout is expected to be a cultural hybrid of some type, whether they have deliberately chosen to meld the concepts of a few cultures from the past, or whether the people surrounding them have simply evolved their culture through osmosis, gradually absorbing whatever was necessary to survive.
In Australia, the common language is English, most of the public records and media are in English, but there are plenty of other languages spoken. Pidgins would develop, out of necessity for immediate communication between ethnic groups that might each use English as a second language. Slang would rapidly take over the mother tongue. Perhaps akin to the fall of Latin, as the Roman Empire crumbled (or the current state of Arabic). English might be the formal tongue, and everyone might speak it at a general level, but in everyday speech there would be numerous dialects. To speak a truly secret language, the denizens of the future might speak a pure language of our time, something uncommon in Australia like Russian, German or Spanish...tongues that are known and are written in enough books for people to piece them together, but which have simply not been needed for survival.
Religions in the setting are similarly appropriated from the fragments of the past. Here is where I would specifically ask players to explain how their interpretation of the religion might change in light of the events that have shaped the Walkabout world. As a Christian, how would you justify your existence in a world where the apocalypse has come and the "rapture" seems to have taken place? As a Buddhist, how do you explain your place in the new world? I might not expect players to consider these questions too much at the beginning of play, but their answers would definitely start falling into place after a few sessions. And I would keep bringing these aspects of the character's belief into question. If all spirits are evil, how do you justify their actions in helping a lost child? Does free will exist? What are the implications of that?
Players are expected to take aspects of the current world; they appropriate culture and adopt stereotypes, to develop a shorthand for explaining who they are in the world. Once this shorthand has been established, the deeper issues can be explored. How much do they actually resemble the stereotypes, and how much to they maintain the façade for the world outside while deeply clinging to other aspects that define themselves?
The conceit of the game is an Aboriginal spirituality, but I could have just as easily made the characters Taoist exorcists, wandering the globe to restore balance using that paradigm, or technocratic-parapsychologists hiding their true system of belief from the last fragments of a monolithic entity crumbling in the face of a post-apocalyptic world where the resources ran dry a long time ago.
There is so much more I'm thinking about for this game, but all of that requires getting the basic concepts working and having the game face the real world in play.