I've got two things
That I don't go out of the house without, to the point that I'd freak out if I didn't have them on me.
Strictly speaking they're not irreplacable things, but as I have them on my person at all times, they mean a lot to me.

My pocket knife - Beech-wood handled carbon steel Opinel Number 6.
This is the most important. It's not that I'm going to stab someone, it's a tool, not a weapon.

Silver ring - Stainless steel ring, right-hand middle finger. Got given it years ago by a girl I knew.
( Cawl, Thu 8 May 2008, 14:39, 7 replies)

You love her, you want her babies
you want to do naughty things to her face and then tell all of your friends.
( Bert Monkeysex is waiting for the mods to delete him, Thu 8 May 2008, 14:49, closed)

Don't talk
About my knife like that!
( Cawl, Thu 8 May 2008, 14:50, closed)

Opinel!
Mine is going on for 20 years old now and still going strong. It, and my original Swiss Army, have both had 'lost' periods and I was overjoyed when they re-appeared.

I could go into my other knives, but people would start to get worried.

I can't carry the Opinel ('Reasonable Cause') and all that, but would be lost without my Leatherman.
(osok Rebel without a clue, Thu 8 May 2008, 14:53, closed)

Opinel = WIN
My dad once bought me one to go in my tackle box back when I used to enjoy a spot of fishing. Nigh-on indestructible and could fillet the fuck out of a trout like nothing else! Wish I still had mine.
(keyboardman, Thu 8 May 2008, 14:55, closed)

The number 6 Opinel
Is 2.7 inches long (blade), and doesn't have an automatic locking mechanism, so (I'm informed by a po-lice friend of mine) it's ok.
I've got "reasonable cause" too, working in a saw mill.

I have rather a lot of knives, but the rest stay at home.
Recent additions to my collection are a pair of Frank Beltrame Switchblades that I snuck back from Prague, and a Fairborne-Sykes fighting knife that I picked up in a rather strange shop in Norwich.
( Cawl, Thu 8 May 2008, 14:59, closed)

Sorry
The Opinel was a strange case as it was a collar lock, but some humourless Home Office tit decided that because it 'could' lock, it was a lock-knife. You'd be OK on reasonable cause though, unless you get a plod in a bad mood.

Spyderco have made a lovely non-locking but friction lined job just for the UK market which needs adding to my collection when I have some shiny pennies again. I had to abandon my CRKT KISS as a pocket knife for the frankly gay Leatherman Micra. Boo.
(osok Rebel without a clue, Thu 8 May 2008, 15:08, closed)

Leatherman Micra?
My (kind of, I think) girlfriend has got one on her car keys.
Bit lame...
On the plus side, the scissors are excellent, more than can be said for the ones on a swiss army knife.
( Cawl, Thu 8 May 2008, 15:19, closed)