Green’s Dictionary of Slang

a sufficiency, a plenitude; cit. 1846 refers to a pickpocket’s haul of money.

1846		Swell’s Night Guide 60: Nummy Ned goes on tout to the gardens, pipes a swell, stalls round him, fam’s him, touches the rumbo [...] Five cooters and a screan ten, and medza croon in white.
1876		C. Hindley Life and Adventures of a Cheap Jack 192: Mo exclaimed to his man, ‘Chuck rumbo’ (eat plenty), ‘my lad, for you will get no more till night.’.
1891		‘’Arry on Wheels’ in Punch 7 May 217/1: Larks fust and larks larst is my motter. Old Richardson’s rumbo is rot.