The students who win those things come up with original ideas, often publishable. The best way to do something like that is to either learn a ton about a particular subject or find a mentor like a college professor to help you come up with and test an idea. The reason it's so impressive to win those is that those students are often doing graduate-level research already. You're not going to get a good idea online that will lead to something publishable. We don't just give them out to everyone, and chances are good you don't have the background to grasp it yet anyway. If that's the kind of competition you want to enter, find a mentor.