The gift is a large quantity of logs.
If you head to Chapter 8 and read about ten paragraphs in, you'll see where Jethro is pleasantly surprised, and somewhat embarrassed, to be the recipient of a gift from Dave Burdow. It's a load of logs: a valuable resource in any situation, but especially now that the war has placed a strain on the availability and conveyance of goods. The logs will be particularly helpful to Jethro and his family, who are in the process of building a new barn. (And if they don't get it finished before the first snowfall, then their animals may suffer without the shelter they need.)
Jethro's reaction to the news of this generous gift helps us understand his character and how it's developing. His face turns red and he struggles to use good grammar as he offers thanks for the gift, and the abundance it represents even makes Jethro capable of forgetting, for a short while, that a war is going on. This intense, abashed yet humble reaction shows us how conscientious Jethro is becoming, and his attempt to use good English shows us how he's trying to rise above his humble background. Also, the fact that Jethro is receiving this gift from someone he barely knows shows us how his kindness has influenced others.