Toddy, the British Army "Norwegian" hot/cold box is well worth the money. These things are built like a battleship. They will keep frozen food frozen for 3 to 5 days and cool and fresh for at least a week. Good for keeping beer cold, or just filling with ice. They make a good camp stool too.
They are also heat proof, they can be used for keeping hot things hot for a long time. That's more useful than it sounds. They have a big spring clamp on the lid which keeps em water/air tight and are designed to also carry and dispense boiling liquids. The British Army use em to fill with soup, tea and coffee and then transport it in bulk out to the lads. The lids of the Norwegian even have a tap for this purpose.
You can pick em up for £15 to £20 in used condition. But beware, the inside of the box is cream coloured and the used ones have almost all got very heavy staining from British Army teabags and Army issue curry powder.
It's rare to see em for sale in unissued condition and if you do see em, they are usually quite a bit more expensive.
This is typical of the issued ones...
http://cgi.ebay.co.uk/BRITISH-ARMY-...Collectables_Militaria_LE?hash=item5191f26822
The recess in the lid is for a ladle, which is often missing on the surplus boxes. They are also issued with 2 matching 10 litre tupperware inserts per box, which are also often missing or in poor condition.
If you're interested and plan to use it for food, then TBH I'd pony up for one like this...
http://cgi.ebay.co.uk/NEW-BRITISH-A...Collectables_Militaria_LE?hash=item3a59221f47
The only caution I would give is that they are pretty heavy even empty and if stuffed with ice, drinks and frozen stuff then they become a serious lump to carry.