We've got a toolbox worth a good bit more than $1000 sitting in our east coast data center (800 miles away) because if and when there's a problem and someone has to show up on site, it's always at an inconvenient hour like 3AM when no stores are open.
Local maps with the locations of Graybar, ADI, etc., marked (dates the toolbox to "before smartphones" eh)
A mini notebook
Sharpie fine points in several colors
Screwdrivers, nutdrivers - actual tools not bits, useful in many cases
Mini MagLite and headlamp holder
Utility knife (do not use for box cutting!)
Xacto (do not use for box cutting!)
6" Bit extension
8" flexible bit extension
Screwdriver bits of all sorts
Pin extractors for connectors that can't be easily extracted without
Scissors
Metal nibbler tool
Surgeon's Clamp
Neon voltage tester
Wire strippers
Terminal crimping tool
EZRJ45 Crimping tool
Set of 3 pliers (multi sizes)
Lock-jaw pliers
9" #2 Phillips bits- Made by Senco for a rapid drywall screw installer, these combine with a power screwdriver as THE single most used tool we have.
22" #2 Phillips bit - unobtanium but very useful for screwing stuff into rack rails you can barely get to
Large needle nose pliers
Curved long nose pliers
Other similar "larger" pliers
4" and 6" adjustable wrench
Milwaukee Power Screwdriver #6546-1 and spare battery - completely mandatory tool to prevent wrist fatigue, can tighten screws with the greatest of finesse due to the variable clutch
Victorinox Swiss Cybertool
Dental tools (picks, scrapers, mirror)
AC outlet wiring tester
Telephone line tester
Tone generator and probe
PDI CT340 Computer Cable Tester
Wire wrap tool and wire
Pencils and a cheap sharpener
Anti-static wrist strap
OK Logic Probe #PRB-50
Tool magnetizer - because the tips of all your screwdrivers should be very lightly magnetized, just enough to be able to touch a screw and lift it out of that awful corner
Digital multimeter
Soldering iron & solder
Electrical tape
Heat shrink tubing in multiple sizes
66/110 Punch Tool
US/Metric Hex Key Sets
1/4" socket drive set and hex bit adaptor for them
Tap and drill sets for common rack, computer sizes (6/32, 10/32, 10/24, etc)
20' Tape measure
Small Hammer
Rubber mallet ("compliance tool")
BIG flat, Phillips screwdrivers ("small pry bars")
Box cutter - utility knife with large handle
Torpedo level
Small drill
First aid kit
Dual D-cell Maglite
Test leads (alligator and hooks)
A decent clamp-on ammeter
A good labelmaker (harder to find than you might think)
Cans of air, WD40, adhesive remover, alcohol wipes, contact cleaner
2" Velcro One-Wrap in the cut-it-yerself roll. There are other options specifically made for tight wiring environments but this stuff is just overall a super-handy consumable.
External DVD-RW drive and a pack of blanks
External floppy disk drive and some disks (yes really, never know what stupid stuff a BIOS update for an odd system requires)
USB thumb drives