A good cocktail often requires a good hunk of ice. I keep these ice balls in the freezer year-round, because they are an easy, inexpensive way to turn out perfectly round, solid ice balls for cocktails. These come 4 to a pack, and you fill up each ball with water then seal it with a silicone cap. To unmold, carefully open and release the ball of ice.
They are not the sturdiest things ever; you have to carefully run water over them in order to get the ice balls out without cracking the plastic hinges. But they are convenient and can be tucked into smaller unused corners of the freezer - unlike an ice tray which often seems to take up an entire rack.