Yes! 
"Thanks Miss, but I'll have the fish instead."
“Would they increase the weight of the aircraft?”
No, and the turbulence from the airflow created to displace
their weight inside the cabin would be easily corrected by
a slight trim correction on the ailerons. However this is
not recommended if the aircraft is flying to close to
the speed of sound. Flys flying forward may break the
sound barrier.
Yes!
"Thanks Miss, but I'll have the fish instead."