Some of the sweet treats we had once a year at Christmas were outrageously expensive back in the 1970s and really meant for adults, not us, though we managed to eat a few anyway: crystalised fruits in a wooden box, marrons glaces, Turkish delight in the box full of icing sugar, a huge box with drawers of Terry's extremely dark and bitter chocolates without any fillings - very grown up and frankly a bit boring so we only ate them to make a stand - and Neapolitan chocolates. These were genuine treats then, and still would be now, in my view anyway.
Chocolate at Easter. Satsumas/clementines (they came in wooden crates, with leaves) at Christmas.
More regularly, a "quarter" of sweets (always sherbert lemons for me) in a paper bag once a week - either eke them out for a week or eat them in one go on a Saturday morning and live with it.
Fizzy pop about once a month, yet we had (one glass of) fresh orange juice every morning at home.
A small packet of crisps was an occasional treat. If only I could remember nowadays that crisps are a treat not an actual food-group, I would definitely be less barrel-shaped.
Eating at a restaurant was a big treat, and so was a trip to the cinema. Once or twice a year (over a certain age) we'd go to the theatre at Stratford.
At boarding school an apple or an orange once a week was a treat. It's lucky none of us got scurvy.