He instructed them to take nothing for the journey, and then sent them forth with authority to proclaim the kingdom of God even as they cured diseases and healed those who were sick. After accompanying Jesus for some time and being schooled in Jesus' ministry, Jesus adjudged the twelve to be ready for commissioning. The twelve had been with Jesus and had watched the Jesus' wayof doing ministry. The success of their ministry was going to rest in their faithful imitation of Jesus which included a very important aspect:  simplicity and complete trust in God . While back-packs, food containers and precious metals would have added to the discomfort of the arduous journey the twelve were to undertake, the instruction by Jesus to "travel light" was also geared towards ensuring success in the maiden mission of the twelve. It was simplicity that was helping Jesus succeed in his ministry. Jesus wasn’t a sophisticated individual. He didn’t complicate his manner of dealing with those to whom he ministered or those whom he encountered. He simply made the best of any situation in which he found himself. He encouraged the twelve to embody such simplicity so that they could remain focused on what was before them. Jesus was only too well aware of how impossible it was going to be for them to focus on preaching the word while at the same time thinking about the food in their back-packs. Moreover, it would be nearly impossible to allow the crowds to press closer to them (as they did with Jesus) if they had such valuables as silver or gold in their pockets. 
Whereas Jesus' instruction could well have been a practical one tailored for traversing the country on foot, it still holds true today for us who have been commissioned in virtue of our baptism. The authority that Jesus gives us is intended to make our message authentic, that is, a message that reflects who we are. The good news that we are mandated to preach must be reflected in how we lead our lives. It would be meaningless to preach detachment from worldly goods while we appear to be holding on to them ourselves. It would be meaningless to preach on divine providence while we ourselves are worried about our tomorrows. This is the lesson Jesus wanted the twelve to learn from the word go. And it is a lesson that we too must be prepared to learn.