Go for food!!!
This is one of the most interesting places in Ho Chi Minh City,  Shopping is good,  bargain, bargian is a must,  but one of the major interesting thing is "Go for real Vietnamese food".  Inside the market food section,  there are many vendors and food stalls.  Most of them are freshly made to order.

In the evening,  You must visit Cho Ben Thanh for dinner.  Sidewalk restaurants serve real Vietnamese food with white table cloths,  the foods are good value and delicious.  You can order all kind of original vietnamese food here, deep fried whole fish is one of the best selections in their menul  Make sure that you do not sit too deep in to the tent,  try to sit outside,  it will be cooler and will make your meal more enjoyable.

When you are in Ho Chi Minh City, try to stay near by Cho Ben Thanh,  this is a central tourist attractions,  walk to the presidentail palace, cathedral, etc.  Visit Cho Ben Thanh for dinner at least one time to gain the memorable experience.