The Ledger allows you to upgrade your camp and even unlock fast travel.

How to Unlock the Ledger

1. Beat the first 5 missions in Chapter 2 and that will unlock Money Lending and Other Sins, a Strauss mission you start from camp.
2. Completing this mission will unlock the Ledger behind Dutch's tent in camp.

All of The Ledger's camp upgrades can be found here:

• Camp Guide and Upgrades