items required:
A cardboard ORICA "presplit" box, or similar heavy gauge cardboard box, plastic bin, fitters toolbox or the boot of the apprentices car.
2 x plastic [mylar?] liners of the type that are in detonator boxes,
A couple of shovelfuls of ammonium nitrate.
Slabs of "industrial lubricant" from wetmess.
Put one liner in the box or suitable container.
Add ammonium nitrate and water to about 1/3 volume,
Sit second liner on top and fill with tinnies of industrial lubricant.
They will be cold in no time at all,
The second liner prevents the ammonium nitrate slurry from direct contact with the tinnies.
Trust me - contact between tinnies and slurry, followed by tinnies and mouth is not a good thing.

After a few hours you can "reboot" the AN slurry by adding more water.
When finished - water the slurry down and dump on the lawn.