The leaf bag is not much different from simply raking up a good pile of forest litter, and sleeping on it - the only weight is a simple groundsheet. The old survival trick is to burrow into a leaf pile for insulation all around. With an envelope of Tyvek (or even an uninsulated sleeping bag liner) to keep the leaves from insinuating into your clothing and to keep out incidental moisture (in the case of Tyvek), you've got a total lightweight system. Of course, it is time consuming and dependent on the availability of materials. Leaf piles in all but the coldest Texas weather are havens for beetles. Noisey buggers that crawl everywhere and tickle.