My kid is too young, but for me:
- academic bowl (primarily on the opposing teams; we were in the same competition pool as the gifted magnet)
- speech & debate (even among the drama kids, who were generally not academically gifted, but had huge tolerance for difference / weirdness - band kids tend to be that way, too)
- high-level (no AP at my school, but what would be AP classes now) classes taken with 1-2 grade higher kids