What does Dave Burdow send to Jethro in Chapter 8 of Across Five Aprils?

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.

How did Dave Burdow assist Jethro's family in Across Five Aprils?

Dave Burdow helps Jethro's family a second time when they are rebuilding their barn.  Although he is not comfortable enough to come to help with the building himself, he sends a wagonload of cut logs for them to use, with his regards (Chapter 8).

Dave Burdow first helps the Creightons when he escorts Jethro home along a dangerous stretch of road where he knows men are lying in wait to harm him.  Because his father was not up to making the trip, young Jethro had made the twenty mile journey to town to get supplies alone.  At the store, some men harass Jethro because his brother Bill is fighting for the Confederates, and Burdow, who happens to be present, perceives that they might try to give the boy trouble on his way home.  Burdow leaves, and waits along the road to escort Jethro through the dangerous area, and sure enough, a man leaps out at the bridge and tries to spook Jethro's horses.  With Dave Burdow's "strong hands on the reins", tragedy is averted, after which Burdow leaves Jethro to continue home and goes quietly on his way (Chapter 5),