Whilst Inverness has all the attractions/facilities of your usual large town & plenty more in the areas around it. Fort William has only one attraction IMO, the Nevis Bakery - Pies to die-for! The rest of the place is grim & best avoided. Head a few miles further south to Appin (top pub by the foot-ferry to Lismore at Port Appin), Benderloch or even Glencoe instead. The Morrisons store in FW is nicely placed on the relief road, by the station so you can easily get in & out fast!
I'd second the South road on Loch Ness too, much nicer than the main road which has restricted views along much of its length & can be quite dangerous to-boot. Especially if you are going North as most parking is on the right. Turn right in Ft Augustus for it.
IV has all the retail you want. A small central Tesco by the main bridge in the centre & a big new one at the retail park by Raigmore Hospital, - well signed from the town & reachable from the Eastern bypass. Lidl & Asda are on the Beauly road at the other side near the mouth of the canal.
Dolphin watching at Channonry point ought to be good, most of the dolphins concentrate on the Moray Firth in Winter.