What do you do in the face of uncertainty? Get more certainty.
And probably the best way to do that is to try working on things you're interested in. That will get you more information about how interested you are in them, how good you are at them, and how much scope they offer for ambition.
Don't wait. Don't wait till the end of college to figure out what to work on. Don't even wait for internships during college. You don't necessarily need a job doing x in order to work on x; often you can just start doing it in some form yourself. And since figuring out what to work on is a problem that could take years to solve, the sooner you start, the better.
One useful trick for judging different kinds of work is to look at who your colleagues will be. You'll become like whoever you work with. Do you want to become like these people?
Indeed, the difference in character between different kinds of work is magnified by the fact that everyone else is facing the same decisions as you. If you choose a kind of work mainly for how well it pays, you'll be surrounded by other people who chose it for the same reason, and that will make it even more soul-sucking than it seems from the outside. Whereas if you choose work you're genuinely interested in, you'll be surrounded mostly by other people who are genuinely interested in it, and that will make it extra inspiring.
The other thing you do in the face of uncertainty is to make choices that are uncertainty-proof. The less sure you are about what to do, the more important it is to choose options that give you more options in the future. I call this "staying upwind." If you're unsure whether to major in math or economics, for example, choose math; math is upwind of economics in the sense that it will be easier to switch later from math to economics than from economics to math.
