There's a deli right outside your hotel, but until you can translate the Scottish names into the simplified names Moira gave you, it's not much good to you.
Did you notice that the restaurant in Giffnock had menus you could take? If not, go get one.
The four items she asked for were haddock, oatmeal parfait, turnips and potatoes, and fudge. Look over the menu and see what you see.
There are a couple of dishes with haddock, but "smokies" are just smoked haddock and nothing else, so that's the most likely for that one. And Nancy will tell you so when you pick it up, which is nice.
Cranachan is described as parfait with oatmeal in it, so that's a good bet for oatmeal parfait.
Turnips and potatoes are surely "neeps and tatties," which, you know, bleah. But okay.
And the only thing that looks like fudge is a "tablet." Great!
So the foods you want are smokies, cranachan, neeps & tatties, and a tablet. That'll cost you 18 pounds all told.