I thought this would be a good thread for comparing ideas on the "spares" box that should accompany you to gigs, large or small. It irks me to hell and back when a band I'm watching has a minor equipment failure, and no plan for dealing with it. So, here's a loadout of my "calamity case" that's been with me to literally hundreds of gigs:

1 spare long guitar cable
2 spare patch cables
1 spare long mic cable
2 mic clips
spare string sets (both for electric and acoustic)
1 pack fuses (for the amp)
1 "Guitool" or similar item
1 string winder
1 power strip
1 pack 9 volt batteries
1 extension cord
1 towel/rag

I'm missing things, but everything I've listed has been a lifesaver at least twice...and the case was either extremely cheap or free, think thrift store. This sort of case should be with every member of every band that remembers it's their job to entertain, not just to look lost when the guitar tosses a string or two.

My wife also made me a padded tube case with some spare foam padding and a kid's plastic pencil box...total outlay was about 3 bucks.