In reply to big_ron:
Can't help you with Portland, but for Swanage:
Have bivvied in the past at Winspit caves - park up near the Square and Compass @ Worth Matravers (an experience in itself) and then stumble over the fields at closing time.
Also Dancing Ledge, not sure if you can do that anymore.
There's a few campsites in/around Swanage.
Good food at:
The Scott Arms - good beer garden, can get busy
The New Inn - Church Knowle
The Anchor - Swanage
Beavers café - Swanage - good for a fry-up in the morning, but gets busy.
The Ship - Swanage
Plenty of places to park up free, depends on how far you can be bothered to walk.