On this page of the guide to Back 4 Blood, you will learn what you can buy with the currency collected in the game, the CP.
In Back 4 Blood, going from act to act, you can collect special currency, which can be spent in the store, located in each safe room. The currency is called CP, they are scattered everywhere: on the ground, in buildings, inside cars...
There are also cards that highlight CP so you don't miss any. In addition, if you did well, you can multiply the earned CP, and then spend it in the store.
The store offers a variety of things. You can, among other things, buy ammo for a particular type of weapon, or buy team perks, which are often very expensive, but everyone can use them. This includes the purchase of weapons and improvements to them, as well as all kinds of accessories, i.e. utility items such as grenades, barbed wire, first aid kits, defibrillators or boxes of ammunition. It is worth to accumulate as much CP as possible to be able to buy more and better weapons and perks, as well as ammunition and accessories.