I am replying here rather than in the 'Teachers don't volunteer' thread.
We call our disbursement system a 'Wish List'. We did this for 2 reasons -- first, so it's easier to say 'no' and second, to encourage people to ask for things even though they might think it is too expensive.
The request flows like this:
PTO Member (faculty, staff, parent, whomever) submits a request
FORM
Request is logged and classified by PTO (in budget or 'general' request)
Requests are passed to the principal. She approves or denies the appropriateness of the item. Sometimes, she denies things because she can make the purchase from the school budget.
Principal approved requests are discussed at the next board meeting
Items in-budget are OK'd for payment or reimbursement at this board meeting
Items outside of the budget are either added to the agenda for the next general meeting or held to be reviewed again at the next board meeting. We delay requests either for lack of information (we want to shop around) or for lack of funds (if we OK'd it, we could not buy it yet anyway)
Requests brought before membership are either OK'd or postponed to the next meting. Parents cannot deny a request, though we could postpone indefinitely if it came to that.
Once an item is approved at a meeting, we reimburse or make the purchase, as funds are available.