Quite by accident, I have discovered the answer to that age old question "How do I eat a Mars Bar without it melting?" Well, I can now reveal the secret!
The normal way to overcome the MMBP (Melting Mars Bar Problem) would be to eat your Mars Bar directly from the 'fridge. However, you are then in danger having to bite hard through the Bar, thus reducing the pleasure of soft nougat and caramel wrapped in chocolate.
So, for optimum Mars Bar consumption, place the Bar into the 'fridge as usual, but remove it from said cooler about 5 to 10 minutes beforehand (this, of course, depends on prevailing weather conditions and the temperature of your 'fridge)
Now when you come to eat the Mars Bar, it will be cool but not rock hard! Just remember to eat it speedily, as it will melt quite quickly.