Having realized I had no broth on hand to cook some greens, I used what was left from a half-empty bottle of Mexican coke (the kind with the real cane sugar). I usually add sugar to offset the bitterness of greens such as turnip or collard, but this actually added a wonderful flavor component to the dish. Offset with some cider vinegar, it was better than weird.
I tried this with chard too (to which I don't usually add vinegar), and while it was good, some bits were sweet beyond pleasantry--you'd need something like vinagar (or at least something like crushed red pepper) to offset it.