Well... the text section on the Vow of poverty does not mention not being able to use items. Furthermore, though the feat text states thus. It makes no provision for WHAT excactly, is a material possession.
Therefor, what can and cannot be used is not specified.
Due to this lack of specificity, any ruling is a house rule, towards or away from strickness.
Legally speaking, atleast.
Interpreting this to the full extent in one direction, the VoP exalted may never eat, because he or she must first POSSESS food, which is material. Therefor, in the literal interpretation of the rules, no VoP until sustenance unless you don't need foor. Neither could she or he use a doorknob (they'd need to beat it into the ground)
On the other hand, at he other extreme, material possessions could be concidered to be only things which they actually own. But then, what prevents them from (litterally speaking) merely acquiring "personal debts" amoung others, and having their things used on their behalf.
The SPIRIT of the law, and a specific and timely ruling on what exactly a material possession is, are important. In essence, we are all relying, to some degree or another, on common sense to define "material possession", and whether or not it must be (as the line explicitly states) merely A material possession to be invalid, or their material possession to be unusable. The rules state none of this.
Pff... law is a wierd thing.