Some years ago (long before I learned to bring everything I needed just in case...) I played in a latinoriented band. There were three guys who sang and played drums and various stringed instruments and there was I playing bass, flutes, bandoneon, etc on my speakerless keyboard.
We had a gig for a big company´s party in a big restaurant with 500 people or so.
We only had to bring our instruments. All mikes, cables, PA, etc were already in place.
When we arrived to the restaurant we found out that they had everything but monitoring. Usually this was no big deal. When we played for 50 people in a big room, I could hear myself in the PA. But now there were several rooms after eachother with about a total of 500 people.
Every room had a little loudspeaker except for the room where we were standing!
During the whole consert (about 1 hour) I heard my friends singing and playing drums and guitars, but I didn´t hear anything at all of what I played. Whenever I tried to raise my volume, people in the other rooms started to complaint about that the accordion (or whatever) drowned the other instruments. So after that hour I was soaking of sweat and without any clue of what I´ve been playing.
Thankfully the audience didn´t care much about our music. They just wanted to eat, drink and talk to eachother.
From this point I ALWAYS bring my Fender passport! (A small portable PA/monitor.)
Michael