I've slept rough a few times without a bivvy bag.
I usualy go for woodded areas, away from footpaths and out of sight of the road. I've never been bothered yet. I have been seen. Once when I slept at Prees Heath after a Mersey 24, but dog walkers don't really bother you. They just want to walk their dog.
I also slept in a field behind a hedge and about 5 meters away from the A41. While I spelt, roadworks were erected. I woke up, then climbed over the gate, to find myself in the middle of some traffic light controlled roadworks.
Be carefull about fields though. Especially in late summer when farmers are harvesting, which is often done at night. Corn fields and the like offer excelent cover, but you really don't want to get tangled up in some agricultural machinary. It won't do you any good at all.
Rural churches can be good, but be carefull now, because churches are more frequently being robbed for their lead now that the scrap value has gone up.
Bus shelters too, in rural locations. Some can be very well hidden from the road.
Wherever you chose to snooze, it's always worth checking out where you are and reading the signs. You don't know whose land you could be dozing on. It could be some millionaire's garden, who owns several viscious and well trained guard dogs.