I saw a documentary a while ago about ancient Europeans and how a body of a viking or something had been unearthed with tools and other things in his grave. The archeologists stated with the utmost confidence that this must've meant that those people believed in life after death and that the deceased could bring those tools with, and then use them in, the afterlife. But how much of that sort of religious stuff did ancient people really believe?
Think about it like this: On paper, America is a "christian" nation. If only a select few pieces of evidence remained from our civilization, depending on what those pieces were, future people may very well think we were all a deeply pious, Jesus-loving people. When in actuality, we love to drink and fuck and do very un-Jesusy things. Even among my Christian friends that still go to church, most only do so on holidays and the few that go every Sunday do so with a wicked hangover from the rage-fest the night before and grumble about it the whole time. Theres a very vocal, far-right Christian movement in this country for sure, but they are the crazy and loud minority. Most people try to simply balance keeping up family traditions with having fun. As a whole, we are far more Homer Simpson, and far less Ned Flanders (and my theory is that we have always been that way.)
So basically: When we find an ancient body buried with tools, did the deceased truly think he would be using them in the afterlife? Or did his kin begrudgingly stuff very good and useful items in his coffin because some high priest would give them the stink eye if they didn't? And are there any candid writings or other evidence from any civilization that had these customs that support the latter?
Thanks in advance!
My reference point is pre-Christian, which has it's own problems, but can shed some light on your question. Ancient Greek religion is largely understood in the socio-cultural terms that /u/Fireproofspider has already referred to. "Belief" isn't a term that really enters the religious equation until Christian times. Also, there were no sacred texts, no clergy or any explicit ten commandment like prohibitions. So, it's a really good context in which to explore your question, it's the ultimate "practiced" religion. The question of whether the average Greek person believed in their mythology, like the labours of Hercules or Orpheus' trip to the underworld, is for the most part anachronistic. Individual cities had their own special gods and myths, but could also refer to the pantheon of gods to participate in the wider Hellenic community. These stories, and the ritual sacrifices and burials associated with them, were the language with which people engaged each other and with things beyond their control. Festivals were their weekends, sacrifices their BBQs, festival performances their cinemas and Dionysiac revels their frat parties. Religion was more ingrained in their lives than we can easily imagine.
This isn't to say that the same social dynamics (Homer vs. Ned) didn't exist. We have great sources from people like Plutarch and Theophrastus who give us each a characterisation of the overly superstitious man. This Ned like figure goes to the temple constantly and consults oracles as to what he should have for lunch, and the audience are clearly having a laugh at his expense. We've also got radicals like Plato who question the very existence of god. So we can imagine some kind of spectrum of religiosity, but the middle is very thick and the extremes are very thin.
So, my take on your questions is that the two aren't mutually exclusive (in this context at least). Maybe people did begrudge losing their best stuff in burial rites, but at the same time we can't extend that all the way to our modern cynicism.