I know this thread is quite old, but there is a large morrisions supermarket right next to the port and also a harvester type pub over the road opposite morrisions. there is a pretty decent pub/campsite aswell about 5 miles away called The Strangers Home
Slightly off topic but when we use Harwich for the trip to the Faroes in the car despite packing everything we're likely to need for the journey we still go into Morrisons and spend more on "stuff", apart from more food we bought an X hose last year off their sales bin.
Oh and welcome to Fun by the way.
And another thing, as said we use Harwich with the car as it gives us a good sleep before a lengthy journey to Hirtshals over the next couple of days but in the van next month for Norway no need for a sleep and a hotel with the van so we're planning the tunnel so we don't have to leave the dog all night. Any particular reason you're travelling Harwich to Hook?
I am coming back into Harwich when I return to Uk after my summer trip and have booked Brookcroft CL. Havent stayed there before but they are apparently 5 mins from the port and charge £15 inc hook up. You do need to be a member of the Caravan and motorhome club.