Halong Bay to HaiPhong airport for taking a flight to Hoian (Less time than Hanoi airport). Flight to Hue or Phong Nha cave, you need to get to Hanoi airport.
My Tho or Ben Tre tour from HCMC, Cai Rang and Phong Dien floating markets in Can Tho and then An Giang - Chau Doc (Tra Su cajuput forest and floating villages (fish farms). From Chau Doc you can take a ferry boat to Cambodia.