why does cash take his tools with him on the trip to jefferson?

THe tools are an extension of Cash,

Cash takes the time to tend his tools.

Although he must be psychologically drained and physically exhausted, Cash "gathers his tools and wipes them on a cloth carefully and puts them into the box" (Faulkner 80). Later, during the family’s trip to bury Addie, as he begins guiding the wagon across the swollen river, Cash "lifts his box of tools and wedges it forward under the seat," thus commencing the dangerous crossing with "his arm braced back against Addie and his tools" (147; 149). Cash thereby demonstrates the same concern for his tools as for his mother's remains in the coffin he had built to protect them.

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He needs to work on the Tulls' barn roof.