Sleeping Bag²
This is an example of squaring two consecutive, identical words:

Sleeping Bag² meaning a sleeping bag bag. 

ie, the bag a sleeping bag is stored in.

When spoken it is standard to say 'squared' rather than 'to the power of 2' or the traditional long form 'sleeping bag bag'.

Putting such words to a power is a handy method in short hand.
'Eugh, someone has spilt lager all over my Sleeping Bag²'