Came across this interesting how-to on creating your own plastic using Milk and vinegar
This is a quick and simple method for making your own general-purpose plastic. The constituent ingredients are milk and vinegar. That’s it. The total cost is less than $10, possibly less than $5 if you can get a good deal.
http://www.instructables.com/id/Homemade-Plastic/
Though I would share
Which kind of milk works best or makes a better ( more flexible) plastic?
Do you have a way to make plastic from soy beans too? It could come in handy if you are marooned on some deserted island! People like us could probably get home by just building a sailboat! 
:graduate:
thx
good question…
Here is a link to some more information on the protein used and its uses through history.