Green’s Dictionary of Slang

cream n.3

anything simple or very easy.

[US]Gleason & Taber Is Zat So? II i: clint: You don’t think it would do Chick any harm, do you, Fitz, to have a little practice go? fitz: Harm? Cream in the can, old boy!
[UK]J. Cameron Vinnie Got Blown Away 71: Sometimes it’s a cream, sometimes it’s a fuck-up.
[US]Eble Campus Sl. Sept. 2: cream – an easy course.