If you're asking as the payor, as BeachBabe said in the last sentence, do you have reason to believe the children aren't being taken care of? That's what it comes down to. If the children are being taken care of, you won't get far in asking for any kind of accounting, even with a judge who allows for it. If you're the payee trying to prove a point, it generally doesn't work. People are going to believe what they want to believe.
Now for discussion, not pertaining to the OP's post...
Many of the items Beach brought up, some will take offense to...like vacations. But any court is going to see that kids, just like parents, need vacations, and its not unreasonable. And if a parent goes on vacation and takes their kids with them, there are expenses involved. There are the clothing, groceries, utilities and rent as you mentioned. There is also added healthcare costs in insurance, prescriptions, over the counter meds, doctor bills, etc. There is that dollar they gave them to get an ice cream, the extra they gave them for a special lunch at school one day when they didn't want the cafeteria food, the gas to transport them to and from daily routines and activities, costs of activities if they participate. And is cable a necessity? Probably not, but do you know of any child in today's world without cable or internet access? In fact, internet access almost IS a necessity per some schools.
So a lot of what people would throw to the wind, a judge will be more reasonable about. They won't discount this stuff just because one parent won't agree with it. Because the judge has no axe to grind with either parent, while a parent may, and in all probability does. And they will often be trying to prove a point against the other parent over the welfare of their kids.