During my visit to the Mekong delta during my trip to Vietnam, I made sure to stop at Can Tho. The first day, I simply watched the river go by and went to the wonderful market of Cai Khê. It is clean and I found a kaleidoscope of the country's fruit and vegetables. At the meat and fish stalls it get a bit more complicated. Besides the usual stalls selling poultry, beef, and pork, there is also a large choice of turtles, wormy looking frogs, slimy eels, snakes, and even the poisonous pufferfish. Its an ugly, puffed up fish which has a very strong poison in its bile. It requires real skill to cook it so that it's edible.
The next day I went for a classic trip on the Mekong. 6 hours following the water, looking at authentic floating markets and wandering down remote canals. You shouldn't miss it for any reason, and the trip is best if you go from Can Tho.