Three pieces that have been in my closet for 10+ years are a pair of skinny pants, a flannel 3/4 shirt, and a long black vest. I have varying reasons for keeping them.
1) The skinny pants are something I'd never buy for myself because they're hideous--the high waist and back side were too big for me, the tapered cut is dangerously close to "mom jeans" status. However, they are insanely comfortable. They've been in the banishment pile following several closet cleanouts, only to be rescued a couple of times. The first time I saved them was because I was going on a ski trip and needed a warm, comfortable bottom layer to battle against the cold. After its purpose was served, the pants went back to the banishment pile. Then the skinny jeans-long tunics trend came around, and I thought the skinny legs of the pants would be perfect. Sure, the fit at the waist is terrible, but a long top would cover it up.
2) The flannel shirt isn't a fashionable item, but I see them around every time Fall rolls around. Perhaps its endurance is attributable to its utilitarian nature--rugged and warm. Also, it's plaid. Plaid can be in sometimes, and even when it's out, it's never truly out. It's just hanging around in purgatory, waiting to return in its modest way.
3) I bought the vest back when I was in high school. Have you seen the show "Ugly Betty"? Yup, I used to dress much like that. Not in such an exaggerated way, but pretty close. The vest languished in the depths of a closet in my family's house for years. When vests recently became trendy, I dug it out, hoping that I'd milk something out of it. Through a little bit of experimentation, I got some wear out of it, but I was hoping it would do something more.
As I said last time, one way to update old items is to mix them with something newer. In my case, I used a newer tunic sweater and my Mike & Chris hoodie. Another way is to wear old items in trendier ways, such as tucking the pants into the boots, wearing a long tunic with the skinny pants, or belting at the waist. Finally, it doesn't hurt to throw all the trends together at once and see what happens. However, this approach is to be used with caution, as sporting too many trends at once may end up making you look like a "fashion victim."
That's my boring little experiment [yes, I actually wore these out to go about my daily business]. Next time it'll be marginally more exciting.