We visited the Somme valley during a week in December.
Many shops (cloths, ...)were closed during the week and only open during the weekend - but this was not an issue for us - because we were looking for a quiet place with a beautiful nature, and some good restaurants. In the neighborhood different remarkable zones are available to spot birds.
Only a few tourists came to this region, so don't make too much publicity for this region... ;-)
(and you even don't have to pay parking costs in the streets of Le-Crotoy from 1/12 until 31/3).
Also Pierre-et-Vacances is an excellent place to stay with a good quality/price ratio, modern furniture and stylish building, clean and all needed material for the kitchen.
Breakfast (croissants, bread,...) can be ordered the evening before but no restaurant is available in the P&V building, some good restaurants nearby.