Bloody simple really;
It's a fat pilot plus lunch box.
If he/she is a thin pilot then the fat pilot left his/her lunchbox in the cab on which ever side it leans.
If pilot has eaten lunchbox then it's the left over tupperware box plus crisp packet and a half eaten apple core (leans less).
If pilot is thin and lunchbox is not present then it must be something else in the boot i.e. crate of beer left over from last do.
If crate is empty the the glass bottles are too thick, change brewery.