I need help from a physics brain: thermal capacity, conduction, cooling...

Lord Monckton

I am doing a zainy experiment at home.
I need to devise a way of applying a cooling intensity factor (CIF) of around 70 mW/cm2.
I need to cool material that is roughly 30 degrees Celsius down to around 2 degrees Celsius.
The cooling has to last for a period of one hour or more.
The surface area of the cooling devise has to be around 100 cm2.
The only equipment that I have at my disposal is a household freezer.
My plan is to place some sort of materials in the freezer, cool them down and then apply them to the target.
Should I use:
(A) Water in a plastic container?
(B) Water in a metal container?
(C) Lead plate covered in plastic?
(D) Lead plate inside a metal container?
(E) Some other household materials or a totally different method?

Please help. I have the attitude of a mad scientist, but struggle with algebraic concepts like thermal capacity and conduction.