A portable shelf includes a planar shelf surface, a cleat, and a strap secured to the cleat. The cleat has a first end connected to a rear edge of the shelf surface and a distal second end. The cleat may either be integrally formed with the shelf surface, or pivotally connected thereto. The cleat is substantially perpendicular to the shelf surface in an open position. The strap forms a continuous loop for encircling a support post. The strap is tightenable against the support post, thereby securing the cleat to the support post.