I've been from Benbecula on the causeway through the Isle of Grimsay, to North Uist many times.
I hope you are used to the many Single track roads on the islands, with their errant sheep...

Which way are you going? Oban - Lochboisdale or Uig - Lochmaddy?

Your Shopping for Highlandwear will almost certainly be limited to the very big towns, most probably in Edinbugh, Stirling, (Oban if you go that way) I never saw a kilt on the islands.

There is a craft silversmiths https://www.hebrideanjewellery.co.uk/ at Iochar on South Uist, near my old Sgoil (now a community centre).

The Dark Island restaurant / hotel on Benbecula was good when I lived nearby but that was some years ago.