My Dad had a flat in Moscow with a window box and decided that he would take some Phostrogen (white powdered plant food) to help nourish his plants.

Rather than taking the box he decided he would decant the white powder into a clear plastic bag and pack it tight in his hand baggage. The cunning smuggler made it through Heathrow but unsurprisingly was cornered at Moscow where entry procedures tokk significantly longer than usual and where his horticultural narrative like his window box withered and died.