Anthropologically speaking, religions are formed for many other reasons than someone's desire to believe in something nice and cuddly after death. Making sense of the unknown and explaining the natural world is a part of it, of course--but only part.
You would also need to consider what rationale is in place behind any cultural taboos your characters have about food, geographic locations, or sex etc. Also, how differently will your societies celebrate marriages? births and deaths? Will they celebrate them at all? How did these rites of passage develop in a secular society? What alternatives would you have for religious festivals, pilgrimages and other methods of social cohesion and community-building? Will your societies have a sense of the sacred at all (not necessarily in a traditional religious sense)?
To be honest, if you're going for a secular society you probably don't need to worry too much about religious references or the above. If you're planning on indepth worldbuilding for societies who have never experienced anything like religion, you may wish to take it into consideration though.
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You would also need to consider what rationale is in place behind any cultural taboos your characters have about food, geographic locations, or sex etc. Also, how differently will your societies celebrate marriages? births and deaths? Will they celebrate them at all? How did these rites of passage develop in a secular society? What alternatives would you have for religious festivals, pilgrimages and other methods of social cohesion and community-building? Will your societies have a sense of the sacred at all (not necessarily in a traditional religious sense)?
To be honest, if you're going for a secular society you probably don't need to worry too much about religious references or the above. If you're planning on indepth worldbuilding for societies who have never experienced anything like religion, you may wish to take it into consideration though.