A quiver is a container for carrying arrows. A hunter might select a particular arrow (considering the weight, the fletching, the point, etc) for a particular prey. In your sentence, arrows and the quiver are metaphors. The arrows represent the firm's strength or capability (technical ability, financial strength, reputation, legal force, etc). When a firm determines what "arrows it has in its quiver", it is considering the possible approaches it can use to solve a problem.