It depends where you start from (North London covers a multitude of sins) but, I'd aim for Brentwood, take the back roads via Padham's Green to Stock then go on via West and East Hanningfield to Bicnacre and Maldon, then via some lovely back roads to Tolleshunt, then on to the northern tip of Mersea Island, take the ferry to Point Clear, then go on to St Osyth, Thorpe-le-Soken and in to Harwich (the road from Thorpe to Harwich isn't a lot of fun, but there are some nice views), take the ferry to Felixstowe, then another ferry to Bardsey, and then Snape, Leiston, Westleton, Walberswick, and take the ferry over to Southwold.
You may have to check out the ferry websites and to call ahead. There's some half decent B+Bs in Harwich, but it might be nice to spend the night on Mersea Island (if you've got the ferry on to Point Clear sorted for the morning).
(later edit) pubs. The Blue Boar in Maldon (the Continental Cafe does a nice tea, and the service is better than the bigger place opposite). Harwich is stuffed with decent pubs. The Eels Foot Inn at Eastbridge is nice. There are nice pubs in Walberswick - I like the Anchor.