So get this. I spent last week hiking the canyons of Sierra Ancha Wilderness in Arizona looking for 700 year old cliff dwellings. This year there was a wildfire on the west side of Cherry Creek Canyon at Pueblo Canyon (the “Juniper Fire” caused by lightning). Hiking the burn area I passed an agave plant that had been roasted whole by the fire. I touched the leaves and what I noticed is that the leaves became waxy and pliable like plastic. They were flexible, but did not crack.
It is very easy to imagine moulding agave leaves into a useful shape then hardening them into that shape with fire, maybe sealing seams with something to make larger waterproof items. Agave could have been used as a primitive form of plastic. Possibilities are endless as to how a lightweight waterproof plastic could have been used.
I ran this idea by the rangers at Tonto National Monument and showed them ny fired agave leaf. They agreed that it was a very reasonable assumption that agave could have been used this way, but there is no way such a fragile artifact could have survives 700 years of decomposition to be rediscovered now.
This is the wonderful part about traveling on foot in the wilderness. The hands-on experience of interacting with the environment with all the senses fosters an intuitive understanding of it that can’t be imagined any other way. Experiencing the context makes all the difference.
I’m curious what ideas you have for prehistoric implements to make with strips of agave plastic. Have you ever heard of or seen something similar in use?
THE ANCIENT SOUTHWEST 
Gourds have been used to make containers, water bottles, etc . . .