A solid pair of 5 kg bumper plates. These are standard in Olympic lifting and CrossFit because they're designed to be dropped from overhead without cracking or destroying your floor (though at 5 kg, they are a bit thin, so you still want to be careful).
Product Specifications
Weight: 5 kg (approx. 11 lbs) per plate.
Material: High-density rubber with a stainless steel inner ring.
Compatibility: Designed for Olympic barbells (which have a 2-inch or 50mm sleeve diameter).