The way I understand it (as it was explained to me by a CM at the walk up food place at CSR (Rix, I think):
You can substitute 1 CS credit for 3 snack credits at a food location (not the gift shop/sundry shop) in order to "build" your own meal. e.g.: 3 items such as a yogurt, a banana and a cookie (3 snack items) would equal 1 CS credit.
My mother had a accidental fall getting onto the monorail on our last day and ended up in the hospital. The 7 of us were unable to make it to the CS meal on our departure day. So- I went to the sundry shop/gift shop to try and exchange for some snacks. They directed me to the Rix Café. The woman there (without knowing our unfortunate circumstances) *encouraged* me to buy up all these snacks to make sure I maximized my plan. I walked out of there with a big ol bag of snacks (fruit, cookies, chips). My mom was grateful for any food she could get after her fiasco at the hospital, whilst rushing around to make the plane home. And, our kids appreciated all the mickey shaped rice krispy treats they got in their lunches after we were home!
I should add...this was 2 months ago.