Hello Niki,
Just in case you were not aware, there are two basic types of cool boxes. The cheaper ones tend to use just electric power, - usually 12V dc and they have a small fan and use the 'Peltier effect'. The others use the absorption principal (the same as most caravan fridges) and can use 12Vdec 230Vac and gas.
Each has pro's and cons, so it is deciding what works best for you.
The low cost Peltier units are generally lighter and easier to carry. They come in quite a wide range of sizes. Although they use 12V, some come with a 230Vac to 12V dc power supply so they can be used on mains, but the main down sides are noise from the fan, and they only drop the temperature by 8 to 10 degrees. Some versions allow you to connect the 12V power so the warm up.
The Absorption fridges are multi fuel. They are generally larger, but they are silent, but quite heavy.
They are better at cooling than the pelteir based units.
I have both for different jobs, but I use the absorption one at home to keep milk and fruit juices cool, and its great for parties for chilling a few beers/wine.