Research the schools that ask you this. Look at the programs that they are proud of that you also participate in, and talk about why your involvement would be great for this program. What skills or experience do you bring to the table? Why would a student at their school want to sit next to you at lunch? This doesn’t have to be as specific to the school as the “Why Here?” question, but should be personalized slightly for each school.
These are some programs that are popular among high school students. This is by no means an exhaustive list of nationally recognized programs. Boy’s/Girls States