Noun: Remnants of cloth kept by tailors usually a perquisite of the trade.
Verb: To steal, to pilfer.
Example use (verb form):
Billy 'Fingers' Smith cabbaged another wallet from an unsuspecting mark.
In the old days (before the internets) tailors of less integrity would steal from their clients by ordering what they knew to be excess cloth. Whole pieces should have been returned to their clients - the tailor was usually only entitled to the cuttings, the cabbage - it was theft to keep this extra.
Hence cabbage turning into a word for theft.