Face off with the dog first. Like you know, they less aggressive ones will back down. If it doesn't, chase it. Sometimes just walking towards it is enough, other times you'll really have to get after it. Its always kind of awkward when the owner is around, but if their dog is off the leash (or out of the yard), they're the ones in the wrong, in most circumstances.
Once at a state park on a trail ride, a large German Shepard came after our horses.. He wouldn't back off so I got my gelding after him. The dog wasn't quick enough and he got stomped pretty good.. Right as the owner comes around the corner talking on her cell phone. She was furious and threatened to call the cops on me.. Etc.. Until I pointed out that her dog was not on a leash and she was the one violating any laws.
I don't know about the vinegar and spray bottle.. You'd have to keep it at the ready which I think would be a pretty big inconvenience, honestly. I also wouldn't want to let a dog get near enough to reach it with a whip, unless my horse was chasing it down.. That's just my take on it.