Here's a pic of my "ice maker" - I discovered these bags a few months ago, which can be filled, tied off (leakproof), and packed very efficiently in my Vitrifrigo van fridge.
This won't meet your needs if you are tailgating or doing something that requires huge volumes of ice. But for people who are just looking for a way to replenish ice on the road, where spillable trays will not work, it's an option.
The ice bags are about ten cents apiece on Amazon.