Can I freeze milk?

yes you can freeze milk, we used to do with (real) baby's milk.

Watch out though that milk expands (like water) when it freezes so leave a space in the airtight container.

It should help cool the fridge, but by how much?

Just been on to the dairy council website and you can freeze milk obviously in a carton not a bottle once defrosted use within two days hope this helps.

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Have frozen semi skimmed milk, many times, without any problem. 

Long  Life  Milk  in  the  TetraPaks  almost  expects  to  be  frozen  !  And  as  DD  says  a  little  shake  before  opening  and  you'll  never  know  the  difference !  Unless,  of  course,  you  forgot  to  allow  it  to  thaw  first 

I've been freezing milk for years in the plastic bottles it comes in from the supermarket without any problems.

Be aware that frozen milk may look more yellowy than unfrozen, but when thawed looks normal

I freeze milk, but i also freeze small bottles of water - not quite full - and a loaf of bread.  I put the loaf in the ice box and the bottles in different parts of the fridge.

We use a cool bag when taking the caravan from storage. We find if it is reasonably full and has a couple of ice packs in we can generally get where we are going with the food still fresh.

Can you not turn the fridge on on gas the night before?

If not, I would invest in an electric cool box for anything you want to take with you, and turn the fridge onto gas as soon as you arrive on site....the gas works better than the electricity.

An hour or so on gas, then turn it to electricity and load up your food.

BTW...yes....you can freeze semi-skimmed milk, just shake it well when thawed.  Orange juice freezes well too.