Tomado del lenguaje del golf, parece referirse a personas sin importancia en la jerarquía que realizan el trabajo sucio o trabajan o cooperan con esa organización, quizá en el sentido despectivo de "peleles", "chupatintas" o subalternos o colaboradores de poca monta.

Por ejemplo:

Already Tony Blair has had a rebellion from 122 of his MPs. That number is now likely to increase with junior parliamentary bag carriers in his team threatening that they too are likely to resign.

http://transcripts.cnn.com/TRANSCRIPTS/0303/10/wbr.00.html

Mr President, the message to the drug pushers, the corrupt, the money launderers and other bag carriers for organised crime should be clear.

http://www.parliament.nsw.gov.au/Prod/Parlment/HansTrans.nsf...

Gratas horas.