What is the Logans' most valuable possession in Roll of Thunder, Hear My Cry by Mildred D. Taylor?

The Logans’ most valuable possession was their land. 

Very few people own land in the Logans’ area, and of them very few are black.  Most of the blacks were previously slaves, and then might be serving as share-croppers working someone else’s land.  In some ways, share-cropping was almost as bad as slavery because a person could never make enough money at it. 

Owning land is hard though.  Even if you do not have a mortgage, you have to pay taxes on the land.  If the land is worth a lot, the taxes can be prohibitive.  The Logans constantly worry about keeping their land.  They depend on crops from the land; they have to bring in money to pay for its upkeep. 

In 1887, when the land was up for sell again, Grandpa had bought two hundred acres of it, and in 1918, after the first two hundred acres had been paid off, he had bought another two hundred. It was good rich land, much of it still virgin forest, and there was no debt on half of it. (Ch. 1) 

Cassie asks her father why the land is so important.  On the one hand, she understands that her family values the land highly and is proud of it, and that people like the Grangers try to get them to sell.  She just does not really appreciate what matters so much about the land because she is young. 

“Look out there, Cassie girl. All that belongs to you. You ain’t never had to live on nobody’s place but your own and long as I live and the family survives, you’ll never have to.  That’s important. You may not understand that now, but one day you will. Then you’ll see.” (Ch. 1) 

To Cassie’s father, the land is their heritage.  It makes them more equal to the whites.  It is also a legacy that he can pass on to his children.  If they do things right, the land will stay in the family for generations.