The ornamental design for side peg boards, as shown and described.
FIG. 1 is a front perspective view of a side peg board on a vehicle, mounted on a side panel of the vehicle's open cargo bed, flush with a surface of the side panel and a top rail of the side panel;
FIG. 2 is an enlarged view of the portion of FIG. 1 depicting the side peg board;
FIG. 3 is a front orthogonal view of the side peg board; and,
FIG. 4 is a top orthogonal view of the side peg board.
The broken lines present in the drawings are included for the purpose of illustrating portions of the article which form no part of the claimed design.