I think one important observation is that it's very hard to distinguish poor because they can't from poor because they make bad choices and don't have the tools to make better ones.
Some comments here point out that while toilet paper at Costco might be cheaper than at the corner store, lack of transport options means the corner store is the only option.
Other comments point out that somebody who is poor might spend what little money they have on bad and/or frivolous choices with that money.
Having been pretty darn poor a couple times in my life, I can say that both are true. I've personally been in situations where the only available options were several times more expensive than the cheapest possible one. I've also (and have known many other poor folks) made fabulously stupid decisions on what to spend our limited money on.
An anecdote, I had a poor friend who was constantly struggling to make his rent and car payments and was in a state of near constant financial emergency. He knew, down to the penny, how much money was in his bank account on a daily basis, when pay day was and all his bill paying days. "Don't cash that check until next Thursday" was a normal phrase from him. And yet when a local fair would come around, he'd take a day off work, gather his family in their beat up used car, buy expensive custom made costumes for everyone and spend the day walking around and spending yet more money.
At one point when he ended up on the wrong side of collection for non-payment of a medical bill I showed him with pretty basic arithmetic that his 2 WoW accounts would cover that bill easily if he cancelled his WoW service -- but there were all kinds of emotional reasons why he couldn't and he didn't and he ended up in very serious financial trouble.
But he also packed his lunch every day, would skip meals, knew the prices of all the local gas stations so he could save on fuel, and wore clothes that were literally falling apart. Then spend $50 one Friday night at a movie premier, or spending $500 on a tattoo or whatever.
It turns out humans are complicated, and poverty/being poor is complicated. There are probably a pretty large number of people who are currently very poor who would be in a far better situation with decent financial management -- but have never had the luxury of learning how to do that. And who would probably be better off with training on how to make better life choices.
For example, when I was putting myself through college, I remember coming to the realization that I shouldn't buy any more entertainment of any sort because
a) I didn't have enough time for it anyway
b) It turns out there's plenty of free and legal ways of killing time
Now I'm not poor (thankfully) and have carried this forward with me. I almost never go to movies or concerts, I don't buy lots of bullshit or useless electronics. I'm selective in clothes and other necessities. I don't pay for cable TV or a land-line phone (neither of which I'd use) And when I feel like blowing off some steam I simply fire up Hulu or a freeware game or youtube or I paint, read a book or watch a DVD from the library etc.
I turned not spending money on stupid stuff into a habit, but it was definitely something I had to come to a personal realization about and consciously train myself for. I still get that sweaty palm feeling when I see a Steam sale or a Humble Bundle. But paradoxically, I have the disposable income to buy that stuff because I trained myself not to have disposable income.
This is very hard to get across to many poor-but-could-be-ok folks because they have strong emotional and irrational reasons for what they do and it's those reasons that are very hard to break.
I'm almost convinced that there's a kind of poverty in otherwise high functioning people that could be "fixed" with a certain mental health and training regime, without any other changes to their financial status.