Wow. I can only think of two gigs I've done in the last ten years without PA support. The first I did with a Peavey Mark 6 XP with a 4 10 and an 18. It was at a shopping center for a car show and we were about 150 yards away from the buildings facing them. My daughter was there and said it sounded fine. (She's been listening to my bands since before she was born , has a good musical background and I trust her opinions over just about any other person I know.) She has no problems at all telling me when I make a mistake or am too loud or too soft.
The other one was at a campground with wide open spaces and I had my SVT classic and an 8 10 for that one. I was told after the third song that I was too loud. (Yes , I turned it down a bit.)
For out door gigs , you want to be able to move a LOT of air , so multiple cabs or 8 10's are your friend there.