Wow, this thread has more legs than I really expected. Interesting anwers, too.
Perhaps I should have disqualified wedding rings. 
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Social Security card (since age 15)
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Hunter safety card (since 1991)
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Rabbit’s foot (age 8-13)
I have the outer shell of a skate bearing on my keychain… it’s been there since I was 14 or 15.
There’s nothing else that goes with me everywhere.
My dad has had a lego-man in his jacket pocket for probably the past 10 years.
Seconded. Though I’m really quite surprised that you and I have been the only ones to mention organ donor cards!
A little bottle of supresssed rage and anger.
That’s because in some states, your organ donor wishes are noted on your driver’s license, as they are in Colorado. No need for a separate card.
You know what, Virginia is one of those states! I’ve known that since I moved here, but I’ve just always kept that old organ donor card in my wallet/purse and never thought about the fact that it’s superfluous! I won’t throw it away now, but maybe I’ll stop carrying it around … I kind of like the idea of my FCC license being the oldest thing, anyway.
I have my original social security card from 1954.
Not exactly a specific item, because I lost an ungodly number of them over the years, but I essentially always had a knife with since childhood (maybe since I’m 8 or so. If you’re wondering why a 8 yo would have a knife in his pocket, I was raised in the countryside, and they were quite necessary to collect mushrooms. I’m talking about this mythical era when a 8 yo could be wandering away from home all day long with nobody worried about him being abducted by pedophiles).
I tend to always check if it’s in my pocket before leaving home. It just doesn’t feel right if I don’t have one. I use it mainly for food and as a screwdriver.
It’s a Laguiole (the shape of the knives appearing on this page matches, but not the brand nor the materials : alloy rather than stainless steel and wood rather than horn. )
Ze link, she is confusing, I saw no knive monsieur.
I’ve had my organ donor card since before they started putting that option on licenses. Actually, since before I had a driver’s license. I’m keeping it. So there! 
Also, the card has an “anatomical study” checkbox, which I don’t think Colorado has as an option.
“Anatomical study”? Does that mean you can choose to donate organs just so that students can probe them? That’s kinda cool.
[momentary hijack] I was at the DMV last week, and they only asked me if I wanted to be an organ donor. I wonder if they have just lumped “anatomical study” in with “save someone else’s life” under the organ donor umbrella? [/momentary hijack]
The oldest thing in my wallet is my birth certificate (“issued at Toronto, June 23, 1980”). I got it in grade 12.
They don’t even mane those anymore. We’ve gone through two changes of money since then, and the $1 bill has long since been replaced by a coin. A couple of years ago, Booker57 came to one of our summer TronnaDope picnics on the Toronto Islands, and he brought a fistful of $1 bills he’d been saving. We were looking at them and oohing and ahhing, like we hadn’t seen them in the wild for years… which, of course, we hadn’t.
In Ontario, that information is on your health card (the ID for the provincial health insurance plan). Mine says DONOR 9Z DONNEUR. I don’t know whether that means I get carved up for parts to help the needy or given to science or what.
Upon further inspection, my Social Security card, which I got in June of 1974.