I have an entire snack cupboard where nothing is over 100 cals
My top savoury picks
Space raider crisps especially the beef ones - about 60 cals
Ditto the Lidl version of Quavers, which are much nicer than Quavers and only about 80p for 10 bags and 65 cals a bag. Keep them in the fridge (sounds odd I know but it makes them really crunchy!)
Plus the usual stuff like seafood sticks, carrot, cucumber - if you need a dip, make something out of quark and add maybe a bit of chilli sauce or something to give it some flavour, alternatively some of the Skinny sauces are quite nice (although they all taste very similar!)
Sweet:
Fibre One cake bars as mentioned above are great, especially if you put them in the microwave for about 15 secs. Serve with yoghurt or low cal icecream (Halo is good but expensive, Morrisons own one is good and much cheaper!)
Aldo do their own version of Fibre One bars
Also
Skinny Whips or Bliss Whip Bars
Skinny Crunch too which are about 75 cals
My absolute favourite are Bliss Crispy Delight bars (only found them in Home Bargains) which are 94 cals of deliciousness

Also Freddos are good if you need a proper chocolate hit and 99 cals, and you also can't beat a Curly Wurly, especially if you put in the freezer as it makes you eat it really slowly!