You can make your own DIY freezer pack by recycling a small plastic bottle and filling with tap water then freezing it at home before traveling. Place this with your bottle of eyedrops in a plastic freezer bag and wrap the whole lot in a small towel for further insulation. In an emergency on a hot day enroute, buy a chilled cold drink can and wrap this up inplace of your frozen bottle of water, it will stay cold for around 4 hours like this. I have a similar problem with storing insulin injection pens enroute, and both ofthe above methods do work.