Last night I read a very interesting history of the first so-called (American) Thanksgiving, which said many of its attendees were not in fact religious and thanking any deity, but that they simply were celebrating being alive and having food! Though some people seem very much to disagree; I've ordered copies of primary sources to check out for myself...
Meanwhile I've read accounts of the traditional British+ Harvest Home, which at least some scholars believe the first "Thanksgiving" really was with all its 1600s British people....