Green’s Dictionary of Slang

crumbs n.

[the diminutive sizes]

1. (US) very small sums of money.

[US]C. Coe Hooch! 119: Tuck that [a cheque] in your sock, Barr. An’ for the love of God, don’t try to thank me for it. It’s crumbs.
[US]Esquire Nov. 70I: crumbs: a small amount of money.
[US]D. Pendleton Executioner (1973) 123: He’s giving them crumbs and making a killing for himself.

2. (drugs) tiny pieces of crack.

[US]Source Aug. 98: He graduated from nickel-and-dime-sized crumbs to moving white bricks.

In phrases

on one’s crumbs

down to one’s last few pennies.

[US]Whip (N.Y.) 29 Oct. 2/3: The man who is too poor to pay a shilling or two to visit our theatres, can gratify his appetite for music, at least, if he will take the trouble to walk down opposite Peale’s, or the American Museum. There he may hear the most inspiring strains free of all cost. How often have we made these places a resort when on our ‘crumbs!’.