If you make a nice big portion of salsa they're free.
Dips are pretty good overall, salsa and houmous without oil (or tahini obviously) are free and you can make a creamy one with quark or zero fat fromage frais and garlic - I usually have them with wedges rather than crisps tbh, but as long as a third of it is superfree it's all free and of course you could always have veggie sticks as well.
Walkers hoops and crosses are 4 syns and ringoes 3 (I think, double check) definitely lower than things like snack a jacks. Sainsbury's do flavoured popcorn that's I think 2 1/2 syns...the salt and vinegar's a bit odd, but the paprika one's nice.
There's a free pakora recipe on the website that's ok and a free raita would be pretty easy to make as it's basically cucumber mint and yoghurt.
I made tortilla crisps once from the wraps that are a B choice, cut them up, sprayed a bit of frylight on and then put on spices and stuck them in the oven...they were ok, but I prefer wedges tbh.
That's all the snacky things I can think of off the top of my head - it's sweet stuff I struggle with more, lol.
Though there is 1/2 syn brownies (I use 30g of sweetener and they're fine).