It depends whether you actually mean snacks, or treats. In the case of snacks I try to go for Free/SuperFree foods, although it's not often I actually feel hungry after meals - they're so nutritious and filling they mostly keep me going.
I always allow myself a treat though. Before SW I could easily sit down to the soaps with a family size bag of crisps, biscuits, chocolate bars, etc. and eat the lot! Now I make more sensible choices, which are within my Syns, yet still feel like a treat. The type of things I go for are:
Alpen Lights: 3 Syns each or 2 for a Healthy B choice. I tend to use them as my Healthy B - one in the morning with some fruit for breakfast, and 1 for on a night with a cup of tea and the soaps.
Velvet Crunch: A great alternative to crisps at just 4 Syns per packet. A real "bargain" Syn-wise, when a standard packet of Walkers crisps are 9 Syns!!
Freddo: Great for a chocolate fix, and just 5 Syns each! Lasts even longer if you pop it in the freezer for a few minutes.
Curly Wurly: 6 Syns each and so worth it! I freeze mine for a few minutes, snap it up into loads of little bits and suck on each bit piece by piece - lasts ages that way!
Cadbury Mini Animals: I find these really hit the spot if I'm craving something biscuity! I get them from the poundshop in a multipack of about 6 - for 5.5 Syns a packet, they're not bad. Plus they satisfy cravings for biscuit and chocolate - two birds with one stone!
The great thing about all of these things is that they're low Syn. If I really wanted I could have an Alpen Light (using my Healthy B choice), a packet of Velvet Crunch, a Curly Wurly and a Freddo and still be within my daily Syns allowance of 15 Syns.
There are allsorts of things you can have! These are the things that really keep me going though - I know without them I'd be craving "naughty" foods that bad that I'd end up cracking and having a mega binge.