What crucial thing has Sam forgotten during his preparations for winter?

Sam's taken a lot of time and trouble to prepare for life in the wilderness during winter. It can get pretty cold in the Catskills at this time of year, so Sam knows this will be a real challenge, the ultimate test of his survival skills. Yet because there are so many things he needs to remember as part of his preparation for winter, it's inevitable that Sam would forget something and that that something would be very important indeed.
It's only when Sam returns to his tree after paying a visit to the town of Delhi that he realizes what he's forgotten to do: stack up a big pile of firewood. It's amazing that Sam should've overlooked something so basic; he'll need wood—and plenty of it—for keeping warm and cooking, right throughout the harsh winter months.