What do the objects that Liesel gave Max when he was sick symbolize?

I like the snow incident. In late 1941, Liesel is 13. On Christmas, she brings pots of snow down to the basement for Max, and they build a snowman, lifting Max's spirits greatly. Soon after, though, Max's health deteriorates, and in mid-February 1942, he collapses, unconscious. He is placed in Liesel's room. Liesel's small acts of kindness and devotion towards Max illustrate the loving bond that has developed between the two. Max has in a way morphed into a surrogate for Liesel's dead brother, and Liesel's desperate fight to keep Max alive is one indication of the development of her character: Liesel is four years older now, and while she has not yet hit puberty, she has noticeably matured both intellectually and emotionally.