put things like milk and medicines in the coolest part of your flat. (understairs for me)
I would get some dried fruit like sultanas and raisins as you only need 30g for a portion. ie less space!
my flat is 650feet square and I have used: understairs space, (not in every flat to be fair) beside furniture in a small gap one tin wide
under dining room table
on top of furniture
other people have mentioned under beds, behind sofas, on top of kitchen cupboards (that was in use anyway) behind books onthe book shelf, behind the kick boards in teh kitchen, on top of wardrobes, at the back of wardronbes. (mine are full anyway)
I have a cupboard beside the toilet that I have filled and the space behind the toilet has toilet cleaner
there might be space next to your washing machine for detergent or colour catchers if you use them,
I have more packs of spaghetti than fusilli as the spaghetti is dense and thin packs and can slip in places.
yeast packs, instant mash/custard packs can all slip in those tiny gaps.