If you are an eastern gray squirrel you bulk up in the fall by eating acorns, seeds and nuts. This results in increased fat reserves to insulate you from the cold and acts as energy reservoirs during long, harsh winters.
These squirrels also cache acorns and other nuts by burying them in the ground. They may not remember where they bury every acorn; those forgotten acorns sprout into trees in the spring.
Eastern gray squirrels seek shelter during winter snow storms and for the coldest winter days. Tree cavities make the ideal shelter, but I have seen them chew bird nesting box openings wide enough to squeeze in for shelter.
When winter temperatures moderate, these rodents come out during the warmer part of the day and forage for those buried acorns. If they are lucky enough to live near bird feeding stations, squirrels use their ingenuity to raid those feeders of sunflower seeds often to the chagrin of its owners.
Although it might seem like a pretty good life, there are many perils even in the winter when raptors are hunting for squirrel for lunch. Foxes are also active at this time of year and if lucky will pounce on squirrels. Despite this, eastern gray squirrels have been successful at adapting not only to the cold weather, but to the suburban environment created by people.