A note to Alicia Avocado: I don't think you can rent caskets (I think there are health codes against that - but I'm not positive).
They can, it's just the 'liner' that has to be new.
I was once studying to be an embalmer....lol
Seriously, with green burials, you need to be on top of things as when a person dies there are all sorts of people just waiting to pump the body full of noxious chemicals right then and there. If the body is pumped full of chemicals it won't be accepted into many green burial sites.
Most of the chemicals injected are to preserve the body and give it more 'colour' for public viewing. However, I'm fairly certain a person can view the body right away privately, then simply have a 'memorial' minus a viewing...which means no chemicals.
Don't need a wood casket at all. The burial I did involved a biodegradable recycled cardboard casket that looked great.