What was unique about the sleeping bag Chris McCandless's body was found in, and why would it have particular emotional importance?

In "Into The Wild" by John Krakauer, Chris McCandless died of starvation and his body was found on the Stampede Trail, in a sleeping bag. What gave the sleeping bag sentimental importance is that it was sewn for him by his mother, Billie. His mother, unknowingly, made something that would become a shroud for him.