Best to go by the train, their in 40 minutes done it a couple of years ago, did'nt go to the so-called eastenders, you get off at aretail park. But drove up and into Belgium as theres a place just across the border for cigarettes. Was about £50 when I went on the train.,
I do three or four cross-Channel shopping trips a year:
Cigarettes/Rolling Tobacco/Cigars in France are about 20% higher than in Belgium (BTW they highest on the Ferry itself) so, for the smoker it`s well-worth the 90 minute round trip upto
Real Tobacco http://www.realtobacco.be/welcome/ in the village of "Adinkerke" on the France/Belgium border....purchases should be made in British Pounds "cash" for maximum savings (they do take credit/debit cards BUT you have to pay Belgian VAT paying with them)
For cheap and convenient Beer/Wine in bulk, I go to
Tesco Vin Plus http://www.tesco.com/vinplus/ 'Cite D`Europe' right next to the Eurotunnel terminal which can be found easily following autoroute signage from the ferry terminals.
There`s easy (free) parking right next to Cite`D Europe and Tesco will also take your order online upto a week in advance (if you know what you want) and have the whole lot ready for collection at a set time of your choosing to save time.

Do 'shop about' for the best deal on day-crossings; P & O have 'online' special offers such as; a car and upto 5 passengers on a day-return crossing and including a free bottle of wine for £19.99.....Sea France have similar tease offers online.
P.S At the Adinkerke tobacco shop they offer free Tea/Coffee/Soft drinks to customers.....and they always have 'Persil' laundry washing powder (in 12 Kg.) giant packs for £8 (ish) which is a great deal.
