Purchase a piece of medium density fiberboard slightly smaller than the inside dimensions of your suitcase. If your suitcase corners are rounded, miter the corners of the particle board so that it fits easily but snugly within the suitcase. Place the cinder block onto a tall work surface, lay the particle board on the block, and then the inverted suitcase over the top of the board; the block will help hold the board securely against the suitcase bottom.
Attach an angled top plate to each corner with four screws apiece. Once you attach the first plate, measure the distance of the plate center from each side of the suitcase. Use these measurements to place the three remaining plates so that all four corners are identical.
Screw one table leg into each of the top plates. Lift the table off of the cinder block and set it upright. Fill the suitcase with items you wish to store and close it to create a flat top.