rock food vs. the good stuff

Meaning:

This terminology is most often used by countryafied children. 

"Rock food" refers to any food eaten as part of a meal...

...while "the good stuff" refers to dessert.

Grown man joking with child: Yer s'pose ta eat yer ice cream first, right?
Child: Naw, youou gawta eat the rock food first n' then you git the good stuff.