You can buy a frio cool pack from frio from the price of £13.00-£16.00 depending on what size you require and the way they work is buy putting the inner piece of the kit into water and allowing the pack to absorb the water and then tap it dry with a cloth or tea towel and put it back in the outer case and then your pens and it will last for around 5-6 days and it is nice and cool in the warm and sunny days as I use one for when I go fishing and I have it close by so that it is easy to get a hold of when I need it and it is cool as if it came from the fridge but you can have a look around on the Internet as you can get a few others that are available to you
