For a small town, Hakuba is surprisingly well supplied with services.
Supermarkets

There are three large supermarkets in town.
Most people will wind up at “The Big” supermarket alone route 148. This is the largest and generally the cheapest in town. Open daily from 9AM – 9PM is has pretty much everything a visitor needs. There is a 100yen shop also on site. This place tends to get crowded in the hours after the mountains close, so it can pay to use one of the other supermarkets if you are in a hurry.
There is a large alcohol selection, and as alcohol is generally cheaper in Japan than duty free, it is not worth carrying bottles with you.
The Hapia Supermarket is the 2nd main supermarket in Hakuba. It is located behind the North Face Outlet just up the road from Hakuba Station. Being owned by the JA agricultural cooperative, the fresh produce is the best in town. Open from 9:30am – 7:30pm, it is less crowded than the Big supermarket, and has introduced a lot of deli products in the past 12 months.
The 3rd major supermarket is Appleland Delicia. Not many people get down this far as it is located on route 148 north of Hakuba Station. Opening hours are 9:00am until 11:00pm. It is the least crowded of the supermarkets in Hakuba and has a very wide range of products.
Convenience Stores

Hakuba boasts 2 Lawsons, 3 Seven Elevens, and a couple of smaller stores. The most convenient for most will be the Happo Lawson. Seven Elevens are located in southern, central and northern Hakuba, but are not that easy to get to unless you have a car. The main chains are open 24 hours, while the smaller ones close from 10:00pm until 7:00am
Post Office

There are 2 post offices on route 148. The main Hakuba post office is about 300m north of Hakuba Station, while the Goryu area post office is about 150m north of Kamishiro Station.
Both have international ATMs, but hours are quite limited, so check opening hours.