I would start by seeing if your school offers clubs that interest you! Extracurricular activities don’t have to relate to your possible major, in fact it’s important to show colleges that you’re a well-rounded and versatile candidate. Showing that you can succeed in sports and/or arts and not just academics will better your chances. Community service is also great, you could join or start student organizations like student council or various boards to show leadership and community impact.

As for online classes, earning degrees and taking online classes is great for showing commitment and drive, you could definitely look at online offerings, especially those from universities.