I always carry a TESCO bag filled to the brim with guitar leads, various lengths/colours etc.
None of them work. But it's great to see the musos trying...
Then they complain to me...My answer....
"You asked for guitar leads, I gave you guitar leads. You're obviously not a very good guitarist then, if you can't tell if a lead is working"
Oh Yes, and bags full of dud batteries.p..." Yes, no problem mate. Have a look in there, Should be one that works"
On the other hand. Go to the local shop and buy one!
(Oh and I've found a company that makes Gaffa tape....Looks the real deal...Doesn't stick to anything. Works every time)
As a gigging musician over 3 decades, The 2 groups of people at a gig who make all the difference are The Sound Crew, and the Security staff.
Befriend them, and all will be well.