I hadn't found any info on KK on this board, so even though this this is not a foodie destination, I thought I'd post about it anyway. I was mainly passing through for a day, but was able to sniff out some good food during that time.
First, I was lucky enough to be visiting during Ramadhan, so the Ramadhan night market yielded a plethora of good street food. Open 2pm-7pm during Ramadhan, located a few blocks inland from Warisan Square. There was a wide selection of Malaysian food, including mee goreng, popiah, grilled stingray, sugar filled glutinous rice balls, nasi campur, nasi kerabu (my favorite), and all kinds of cakes. If you happen to be visiting during the other 11 months of the year, I heard the Philippino night market has good street food. I skipped it because I was headed to Manila the next day.
Second there is a wet market near the water, close to where the boats are all docked. There is a separate seafood section in the back (closest to the water) and I also found fruits, vegetables, spices, and other dried goods in the front (closest to the street). In particular, there are a number of places to get dried shrimp or dried fish. The second floor of the wet market houses about a dozen food stalls, where you can get a good inexpensive meal.