I've had the same idea too and I'm wanting to make a campaign about this type of setting. What I was thinking of was maybe having different kinds of tribes like either having a dragon born tribe and an orc tribe where all the races are there but just in very early development or if you want just more of basic humans scurrying around then that works too with all the different sub races of humans there are. I really like the idea of the lizardmen trying to kill you since they would probably work really well in this type of environment. You could also have the early Yuan-Ti that sacrifice humans to their god/gods. Also you'd need flint to light fires and instead of buying rations you'd need to go out and hunt animals for food along with hunting them for their hides to use as armor and their bones as weapons. Like a mammoth toe hammer or something. So far that's all I've thought of but it's really been on my mind lately.