I have a set of those things that hang in the bolt department at Lowes or Home despot. Its a cable with a bunch of threaded rods on it. Each rod has male and female threads. Here's the link to Enco:
Thread Detective
I have found this really helpful, even for sorting my own messy stock pile of hardware.
Other tools I use often are my 12' stanley tape measure. I remove the belt clip as this is small and light enough for my pocket. I was in a lumber yard once and whipped out the big yellow 25' carpenters' tape and teh guy who worked there said "whoa! what are you going to club with that? Put that away". He they got out the little chrome stanley. Everybody needs a good 12' tape.
I also use the heck out of my chinese 6" digital caliper (despite having 2 FAR better models).
For various jobs around the house and car, I use the heck out of my Starrett 4" double square (#13A). Also shown is the 6" version (#13C) and the tiny diemaker's square. I use the 4' most.
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There are couple other cool tools in this picture:
That's a Starrett hard head junior 4" combination set
There is a pair of Starret bevels
An old Starrett depth gage that also functions as a bevel and a pair of carbide tipped scribes, both Starrett.
Obviously, these are metal working tools and now mostly obsolete, as hand layout is mostly a thing of the past. But the double squares are really helpful for all sorts of jobs. And you'd be surprised by the number of "squares" I've encountered, that simply aren't square- like not even square enough for carpentry.
