You can, of course, use any other soft, thin items like socks, lifting straps, even sponges, but don’t use a hard item like a 2.5-lb plate. If you set the bar down, and it glances off that item, it will come back at your shins, and shins and horizontally moving barbells don’t get along well (hint: the barbell always wins). In addition, the contact between the plate(s) on the bar and the 2.5-lb plate on the floor may cause one or both of them to chip. Wrist wraps are thick enough to immobilize the bar but soft and compressible enough that setting the bar down on top of the wrist wraps won’t cause any problems.