There is nothing wrong with your 2yr old son wanting to play dress up. It is perfectly normal.
Why is a necklace considered "girl stuff"? I'm pretty sure men (real men, manly men, men who are not gay, men who are gay, athletic men, artistic men, pretty much any kinds of men) wear necklaces. And rings and earrings and bracelets. And boys of all kinds play with dolls (ok, they call them action figures, but really, they're dolls aren't they?) I don't understand why we need to have "girl stuff" and "boy stuff". It's all there to help nurture the kids' creativity, so why can't it all just be "kids' stuff"?
The only reason I wouldn't let my kids wear my jewelry would be because I wouldn't want them to think it's ok to play with my valuable stuff. That's not "kids' stuff", it's "grown-up stuff" and it's hands off to them!
I wish I had advice to give you. Unfortunately, if THIS upsets your husband so much, he's pretty set in his ways. Changing his perception of how a "man" should be will be very difficult. It'll mean he has to change some basic things he sees as "true". I really hope he doesn't turn out to be the kind of daddy who gives his *son* a "doctor's dress-up" set and a truck and his *daughter* a toy vacuum cleaner and a crown.
I guess all you can do is just keep telling him that there's nothing wrong with kids of either sex playing dress up. It won't screw up your child. If anything, it'll foster his creativity.