Well... if we don't count things I had little control over (halloween when I was about 5 when my mother dressed me as an old lady, or the time my sisters dressed me up when I was even younger), I'd say the first item I was attracted to, when I was 8 or 9, was pantyhose.
I really don't know why, and I don't even think there was much of an element of 'crossdressing' to it back then. It was more just curiosity about what they were and how they felt.
Of course, pantyhose lead to panties...and pantyhose and panties aren't complete without a dress or skirt. Before I knew it, I was putting together entire outfits from my mom's closet or bags of clothes stored in the attic.
I guess you'd say that for better or worse pantyhose were the 'gateway' to everything else.
It took me YEARS before I wore a bra for any reason other than curiosity. I just never saw the sense to it since I didn't have breasts. Now I don't feel dressed without one.
Makeup took even longer. It has only been in the past few years that I've really started learning how to use it and building a collection of it. I think for the first 20 years of CDing, I never touched it except for the occasional quick dab of lipstick.