I wouldnt never claim to be at Pete's level of skill when it comes to packing stuff in the rear of a mini. The amount he fits in the back fo the roadster can only be attributed to black magic.
But for a mini euro trip I think I've packed plenty into the little coupe.
1 double airbed
1 sleeping bag
2 goose feather pillows
2 20L wash buckets with grit guards
1 bag of every cleaning product necessary
1 large bag of microfirbes (various piles)
1 holdall with changes of clothes for every day
9 bottles of Lipton ice tea
6 cans of blood orange San pellegrino
And a litre or so of oil (because mini)