4 answers
In my experience, it matters much more what you can accomplish in an activity, rather than the activity itself. Instead of choosing an extracurricular that stands out, find an activity you are passionate about and stand out by being one of the best at it. In short, the best extracurricular I can suggest is one that you love.
But if you want a specific one... rowing. Rowing is a thing. Colleges seem to love rowing.
As a home schooled student you are allowed to join the clubs at your local high school. One of our best competitors in my TSA chapter is home schooled. Obviously only do this if you feel comfortable but colleges might appreciate the initiative. They will see that you took advantage of every opportunity including ones that were inconvenient. Otherwise, you could look for competitions for individual students that do not need to be through a school. For example, if computer science is your passion, do a hackathon. Try to pick specialize in something. That doesn't necessarily mean drop your other ECs, but try to get really good at one of them.