Here's a beach stroll we did in March 2005. It's on North Uist, only about 4 or 5 miles south of Berneray. You can see different sized versions of these pictures on my Flickr page.
Get off the bus at the sign for Clachan Sands and wander down the track to the beach, between the old and the new graveyards. At the beach turn left. This is what you should see:
Amble along the beach. It's vast, clean, and the only noises you will hear are the waves and the various birdlife. Maybe the distant moo or baa of farm animals, but that's it.
Keep strolling. If you have binoculars, you can check out the islands such as Boreray (previous picture).
You should be on your own, unless you are very unlucky. The highest number of people I've seen on this beach at any one time is 8. Which, for here, is "seriously crowded".
Depending on the tides, when the beach comes to an end you may be able to hop across to the island of Orasaigh. Sands in estuaries out here can be treacherous, so watch yourself.
Orasaigh is a small island used for livestock by local crofters. The highest summit is, erm, 70 feet which is where the above picture is taken from. On here, you can get a good view back up the beach, and further along North Uist to distant Harris.
Again, watch the tide. Once it starts coming in, you can't get back to the beach. Walk across the island and over the tractor track to get to a knobbly bit of North Uist. Follow the shore round till you pass a house (Alastair the bus driver lives there: say hello) and then get back to the North Uist circular road. Turn left, and follow it to the t-junction back to Berneray.
Total walk time: who cares. Take a picnic and some gin and make a day of it.