The video above is an interesting challenge to the morality of how we live our lives day-to-day in the industrialized world. It plays upon a bias we all have-- that we do not have the same moral obligations to people who we don't interact with. We all have this bias, but the question is whether or not it is ethically justified.
If you accept that that bias is not, then it makes ethical sense to do your part in helping the less fortunate. Some go to extremes, such as George Price, as described in this fascinating podcast episode of Radiolab:
Why do I say Price went to the extreme? Because he was a brilliant man who could have helped the world in better ways than simply by donating his money.
I'm one of those people too. Science is good for the world (I am not going to argue this here, but I have my reasons for thinking it), and I'm a scientist. And the fact is that a certain amount of material stuff helps me be a better scientist.
For example, I do most of my work on a computer. If my computer is old and slow, then my productivity is hindered. This happens for two reasons: 1) I get frustrated with the computer, which makes me less productive and more distracted, and 2) even if I were completely unemotional, a slow computer slows down everything I do. So for me to maximize my good effect on the world, I should have a good, fast computer.
In general I try not to be materialistic. I try to remind myself that I have everything I need and more. I try to think of people who are as happy as I am, but who have much less. Thinking like this helps keep me from buying too many things. I try to donate a percentage of my income every year to a good cause. Last year it was "Kenya Help," run by a trusted friend in Kingston, Ontario. If you are looking for something to donate to, I recommend this.
But I don't put on the brakes so much when I want something material that will help me be a better scientist. Computers, books, travel to conferences, etc. are things that cost money. Purchasing them hurts the environment (in the short term) and sometimes is a waste. But if I'm too risk averse with such purchases, I'll hinder my scientific impact.
My conclusion is this: try not to be materialistic. It's bad for the environment, usually, and doesn't lead to happiness. Donate the money you'd spend on things to people in need. This, it turns out, actually does lead to happiness. But if you are doing something really good for the world that requires stuff for you to work at capacity, then go ahead and buy what you need.