Doing something meaningful, in the way you described it, looks a lot to me like guilt over a perceived unfairness of life. Yes people are dying in remote places, yes people need healthcare in the US, and yes not everyone has a job. You want to try and fix the situation, but many others also have tried, and failed.
Maybe you want to do that to be relieve of your guilt, to try and find happiness instead. I mean it's very popular to say that you are trying to change the world, making it a better place, and so on, but then in the end, will it make you happy?
And even worse- what is your final objective? Being happy?
Maybe you perceive a dysfunction is the way the world works vs how you think it should work. Then your goal might be to "remove biais", or be "less wrong". Some blogger might help you in your path.
If your goal is finding consistence, there are many ways which do not always involve doing "something meaningful" in the sense of charity work. Abstaining from charity and being vocal about it, trying to make more people join such absentionist movements, might be very positive. A lot of people believe the problems for exemple in Africa are due to foreign involvement creating a long lasting dependance on aid, food, and so on. Basically, it might not be good to have more people on a continent that can be fed by the production of this given continent. Here the lack of action would have dire consequences in the short term, but would improve the situation in the long term - and it would be self consistent.
If you goal is happiness, a better shortcut might be finding happiness without having to resort to such a guilt-ridden trip of charity, ie learnt to not care anylonger!
If your your goal is being popular, ie respond to peer pressure which views charity work in a positive light, maybe you could find some other way that is also well received - say american idol, a free software project that'll make you famous, fight again racism/global warming/whatever is popular these days.
But from what I have read in your message, I would sincerily question your premises.
Instead of doing what is better "for the world" or "for the global good", have you considered the possibility of doing "what's fun", "what you like", or "what is important to you"? You do not need justifications or moral endorsement to do that. Yet it requires some serious introspection.
If you do have considered these alternatives, and if you are sure of your premises, have you identified limitating beliefs, ie the reason why you consider these alternatives not to be worth your limited time on this earth?