A vertical ice tray
Ice cube trays take up a lot of room in the freezer. The Iceorb makes ice cubes in a vertical tray -- and does a few other things as well.
I used to have four ice cube trays shoehorned in my freezer along with everything else. When I wanted to make certain that I would have extra ice cubes, I'd put ice cubes into a plastic bag so that I could make more. It wasn't exactly a great system.
The Iceorb offers a few benefits, though: it can freeze 21 ice cubes at once, and it does so on a vertical wall, so that I can still get other stuff into my freezer. The ice cubes also won't freeze to anything I stack on top of the Iceorb. It also can store ice cubes--up to 51--if you expect to need more than you might normally have on hand. The ice orb also acts as a cooler: you can stick a bottle of wine or another beverage in the Iceorb before serving or fill it with dip or other foods that need to be kept cool.
It's plastic, so there are no worries about hauling it along on a picnic--and the Iceorb is dishwasher safe as long as you stick to the top rack. It has three parts: the actual ice cube 'tray,' a cup that fits inside the ice cube compartment, and a lid. The Iceorb costs $16.