It's expensive there. But your home country would be, too, if you had to import most everything and provided your citizens with great benefits.
Alcohol is only available in restaurants and the state-run liquor stores (Rúsdrekkasøla). Who wants to waste valuable sightseeing hours trying to find liquor stores that close at 17:30? Stock up at the airport when you arrive instead.
Most rental cars we saw were manual transmission; if you want to ensure an automatic transmission, make sure to specify this when booking your rental.
Take-away options are limited; eta in Tórshavn looked good but hours were limited.
Supermarkets are open until 8 or 10 (but not on Sundays) with some sandwiches available or options for improvising meals.
Things close early.
Keep your speed under 90 km/hr. Watch the sharp curves. Locals will not hesitate to pass you.
You've read about the rules in one-way tunnels; the same rules apply on single-lane roads.
Familiarize yourself with roundabout/traffic circle rules.
Heed the old saying "Red in morning, sailor's warning; red at night, sailor's delight."
You will get muddy and you will step in sheep poop.
There's cell phone coverage everywhere, if you have international coverage. See comment about benefits above!
You will find a well-maintained, free WC in almost every town. Ditto re: benefits.
The wool sweaters for sale are not soft.