Aldi's version of Quavers are only 3 syns per pack. I always have those in.
I recently discovered Aldi's chocolate covered rice cakes and I prefer them to a Freddo as they're more substantial. 4 syns for one. If you'd have told me a year ago I'd prefer a rice cake to actual chocolate, I'd have told you to give your head a wobble!
I have a thing for Aldi's sweet shop lolly ices, or whatever they're called. They're tiny but lovely. Bubblegum, candyfloss, and apple flavours. 2 syns each.
The classic SW snacks: Freddo - 5 syns, caramel Freddo - 4.5 syns.
Most rich tea finger biscuits are 1 syn each. It's nice to have a few of them with a coffee and not have blown my day's syns.
Werther's Originals are my current favourite. 0.5 each for the sugar free version, which are only fit for the bin so don't bother. 1 syn each for the proper ones and they last ages.
Sainsbury's do a bag of sugar free marshmallows. I don't go often, but I make a point of picking up a few bags when I do, as you get 25g for only 3.5 syns, which is loads when you weigh them out.