Here are some of the things in my gig bag:
-Sharpie and paper for writing setlists
-Flashlight
-Spare compression driver diaphragm (for monitor horns)
-Mixing console manual
-Electrical tape
-Pee Chee folder (remember those from 20 yrs ago?) containing: notes for live sound, note frequencies (great for taming boom in a room), common freqs that tune up drums, bass, guitar, vox, etc., and song lyrics
-Cds for PA lightoff and break music
-Spare mic clip
-Spare mic (SM57)
-ConducTool (cleans ¼ m & f connections)
-Rack screws
-Zip ties
-Tweeter bulb for Goliath horn
-empty 9v packages (oops)
-Ibuprofen
-Misc. dustbunnies &grime. Oh, and a good coating of bar smooge on everything listed above (that smoke/beer stench that perfumes everything so nicely for you)
Essentially, just enough stuff that it hangs out the top and I will never be able to properly close the bag. Ever.