Best cases when out in the hot weather with cooling gel or something cold?

If so, what is the best case in your opinion and why?

I have been told I will probably not need one, but I know we want to go sightseeing this summer and I would rather be safe than sorry.  We will also not always be by the car, so I do not want to rely on something in the car.  It needs to be small enough to comfortably carry, but not too small it will not hold my 2 pens, meter, strips, lancing device, etc.

Any suggestions?  Thanks