If you are getting a hire car from Inverness airport, stop at Tescos en-route to Inverness for any groceries as it is the one decent supermarket you will drive past on the way, it's open 24/7 including all Sunday night. Otherwise Fort William has a few too. The little local supermarket in Fort Augustus is great but not open late. It is open 24/7 including all Sunday night.

Some sat nav's will send you further than you need to go using the postcode,

Its just 200 m after turning off the main road, if you get to the fish farm you have gone way too far!

Old school directions:

Once you leave the A82 and join the A87 at Invergarry, drive another 10 minutes towards Skye.

Turn left on the Tomdoun Road and Caledonian Cabin is just 200 meters down there on the left, you cant miss it!