Yes, there is no need to use milk powder. For me, if go out for less than 2 hrs, I will bring one bottle of cold milk from the fridge directly. If more than 3 hrs, I wll bring more bottles of cold milk with "fridge-to-go". (My boy is now 10-month old, fully fed by breast milk, everything is fine)
However, you can buy the travelling packs of Japanese milk powder from www.birth.hk at Jordan.