Since I just discussed fusion energy in my last post, it seems natural to continue talking about possible future sources of energy. Here's an article from Scientific American about turning plant sugars into gasoline. Biofuels are becoming more popular, but by turning corn into ethanol, you reduce the portion of the crop that becomes food. This Madison scientist has found a way to use a variety of plant sugars, including polysaccharides we can't digest. He doesn't produce ethanol, but actual gasoline. (What's really ironic is that he was trying to find a source of hydrogen for hydrogen cells. Sometimes science makes more progress when you obtain an unexpected result.) His process is faster than ethanol production, is carbon-neutral, and can produce other types of fuels, like diesel and jet fuel. It does require certain rare elements as catalysts, and the reaction requires heat and pressure. But once the process starts, the heat it gives off helps to drive the process.
How a society powers itself can play a role in world-building. I think fuel production like this would work well on young planets that can sustain life but haven't done so long enough to build coal and oil reserves. If the planet happens to have an abundance of the catalytic elements, all the better; maybe it could even export them to other worlds. A planet could have high tech like this yet still have a major agricultural component. (And if a society has access to "easy" energy sources like this, it may affect how fast they grow and what their technology is like.) If humans find inedible plants on other worlds, they could possibly harvest them for fuel instead. Or they may find microbes that have evolved to produce gasoline as an energy source or waste product. What would energy do for your world?