Or it’s possible that he didn’t buy them.
I have heard or read the following:
It was discovered at school that Trevon was in possession of a flat blade screwdriver and women's jewelry in his backpack. He didn't get into trouble for it. He claimed it belonged to someone else. At the least it is likely that Martin was friendly with someone doing B&E and burglary. It is also possible he was doing this himself.
As Trevon was walking through the neighborhood he was near houses. Someone who has seen the neighborhood said that he may have simply been avoiding the rain by walking under awnings instead of the sidewalk.
But what if...
What if he did not go out for candy, but was intentionally roving the neighborhood. Zimmerman claimed he was not following Martin after leaving the car, but unintentionally came in contact with him as he tried to get a specific address for police. Zimmerman would not have looked like just another person walking around to Martin. And if Martin was casing houses and realized he was being observed it would be reasonable to expect that he may attack Zimmerman.