Green’s Dictionary of Slang

cream crackers n.

[rhy. sl. = knackers n.; ult. see prev.]

the testicles.

[UK]‘P.B. Yuill’ Hazell and the Three-card Trick (1977) 91: You got me by the cream crackers, I ain’t likely to cross you, am I?
[US]Maledicta II:1+2 (Summer/Winter) 118: He [...] also lists: [...] Cream Crackers Knackers [balls].