##Build Solar Panels ... in SPACE
Well, when you think about it, no matter what resources we use here on Earth, there is this giant power station (a large cloud of hydrogen which seems to have caught fire) a few minutes away.
Think about it. The average whole-humanity consumption is about 16TW (in 2010), while the Sun shines about 174,000 TW on Earth alone, and about $384.6 \times 10^{24} W$ more into empty space each second. That's an unimaginable amount of power, and virtually every Joule of it is waste every second.
So the best thing you could do for future generations is to start creating a Dyson cloud of solar panels around the sun, and use that surplus to power a space industry to build more and more and more!
Once the Dyson sphere is built, you can store your excess power as antimatter in containment fields, collossal flywheels, whatever. But you'll have zillions of times more power than you did before. In fact, it's irresponsible not to do it. It's the only way we could have enough power to move out of the Solar system if we decide we don't like it here anymore, or the sun (billions of years from now) goes dark.