As an atheist growing up in the Bible Belt I certainly knew about the religious aspects of the holiday, but to me it’s always been a family holiday, with presents and lots of food that’s not exactly good for you.
I’m a life-long atheist, never been baptized. (By the time I came along both my parents were atheists themselves. My father is the son of an Episcopalian minister, and grew up saying he was going to follow in his father’s footsteps, but lost his religion in college. My mother has also never been baptized–there’s a strain of irreligion on my mom’s side of the family going back several generations at least; her mother was a life-long matter-of-fact non-believer; I doubt my grandmother would have used the “a-word” but she just didn’t believe in any of that stuff.)
But, we still “played Santa Claus” when I was a small boy, and we had a Christmas tree (with a star on top, not an angel–I guess you could say it was the Star of Bethlehem, but to us it was just another pretty decoration). We always went to visit both sets of grandparents at Christmas time (and as a result often ate a meal at Waffle House on Christmas Day–if we’d spent Christmas Eve with one set of grandparents, we’d typically spend Christmas Day with the other; fortunately, they mostly lived not too far apart, as American road trips go, when I was growing up). Those visits to grandparents also meant seeing lots of aunts and uncles and cousins, probably for the only time for that year. (Partly of course that was just a question of everyone having a block of time off from work and/or school.) As a kid I always liked displays of holiday lights, the gaudier the better.
Later on, after I was grown, my parents formally swore off participating in gift exchanges with other adults, not out of any religious conviction, but as a push back against an over-commercialized holiday, and a desire not to have anyone else waste money on buying gifts for them that they don’t need or even want. (In my mom’s opinion there is an exemption for food, though.) With all my grandparents now dead, I no longer attend any big family get-togethers at this time of year (family reunions, mainly on my mom’s side of the family, are generally in the summer nowadays) but I still associate the season with family and food. (And I still like the more tasteful displays of Christmas lights, too.)