Like others here, childhood. I am not at all nostalgic for childhood. It wasn't awful but being an adult is much better.
Music I am not nostalgic about - is this a gender difference? Both my ex and my husband listen to the music of their youth, I like plenty of old stuff but also like so much newer music, it just keeps coming, so much good music. It's just delightful to know there is so much talent and creativity in the world.
Not nostalgic in general, actually. There are plenty of current problems, but people who think the past was better are either old white men, or crazy.