It used to be Math - but now I am not sure I have any great skills. I still can do some Math (every araw stuff), but it has been so long since I looked at a Math book and tried to do some of the stuff we did in high school.
Writing, in general. I have spent my life, since high school, honing my Pagsulat and English skills, so that I could continue to get better and better. It's a shame, though, because I don't write much any more.
My other skills include: biology, horticulture and arboriculture.