The people over at Homestead dreamer have put out a great guide on alternet things that can be used instead of tinfoil for cooking foods. I highly recommend you check them out.
“Before the invention of aluminum foil, people used leaves and other things to cook food in the coals or on hot rocks around the fire pit. Some are also used to steam food or wrap before boiling to keep the ingredients together. Learning which natural ‘tin foil’ is available in your area can not only give you some new flavors and cooking methods to play with…”
Here is a link to their page and the full info.