As a Leith resident I would probably avoid the Royal Yacht – it is kinda interesting but not really worth the money and is accessed through Ocean Terminal which is the haunted site of a dying shopping centre. It’s a bit desolate round there.
Rocksalt is nice as mentioned, as is Nobles, both on the same street.
The Roseleaf Cafe Bar is nice as well, and do good food if you’re looking. Great fancy Scotch eggs.
William & Johnson inside the little mini arcade thing at Customs House is very nice for coffee albeit quite insufferably hipster (like me). You can sit on the side of the canal basin and drink it if the weather is nice.
Just walking around the Shore area is really nice tbh. It will be a very different feel to the rest of the town as the festival hasn’t yet reached down here but still very nice. If you fancy a drink if you are that way inclined, there are loads of great pubs too; Teuchters Landing for example which has nice outdoors seating over a bridge.
You can get the tram down from the centre of town to the Shore – just make sure you buy your ticket before you get on from the machine at the platform – it is £2 and contactless, but *can’t buy one on board* and they will fine you £10 if they catch you. Otherwise you could just walk down Leith Walk for 30 minutes and you’ll be there.