My Gig bag is trans-instrumental and only contains items apart from what I call "Instrumental Necessities" - eg my fiddle cases hold spare strings, rosin etc and my melodeon case holds stuff like music books, railway magazines etc.

Gig Bag Contents:
Cheapo guitar pickup used for Fiddle
Pink String to tie fiddle to amp
Fiddle stand
Fingerless gloves (2 identical pairs - Vile green (left) and Putrid Pink (right
Music Stand (Church)
Sheet Music transposed to G or D (for Church)
Multitool with Bottle opener (not for Church)
"Essential Band Equipment" (Beer - also not for Church)
Tatty copies of Primrose Polka in D and G(I still have difficulty after all these years and can never remember what we actually play it in)
Electronic Tuner
Fiddle Chin rest (OK - I lied about all fiddle bits being in my cases, but I only just found this in my "not gig" bag
Emery Paper (Don't ask!)
Spare 9v battery

That's all folks!