The Barge pub at Honey Street, Alton Barnes, has camping facilities at the back (£9.00 a night last time I asked). It's situated right by the canal, has a garden with a view of the White Horse and there are plenty of nice walks close by. Avebury is about 10-15 minuets' drive away and Marlborough a bit further. The Bridge pub is close by (also situated by the canal) and does pretty good food.