Hardtack is a type of cracker or biscuit that was commonly eaten by sailors, soldiers, and other people who were required to travel or work in remote locations where fresh food was not readily available. This made it an ideal food for pioneers to eat while travelling via covered wagon.
Laura mentions baking hardtack for Pa to take with him when he was travelling to their new home in De Smet, in By the Shores of Silver Lake.
It is made from flour, water, and sometimes salt, and is dried and baked until it becomes extremely hard and dense. It can be stored for long periods of time without spoiling. The downside is that it is very bland in flavor.
Hardtack has seen a bit of resurgence in recent years as a food that can be stored by those living off the grid or returning to a more pioneer lifestyle today.