http://www.myprotein.co.uk/mp-max/foods/beef-jerky-(50g)/
Low in calories, fats, and sat fats. Only a small amount needed to fill you up as high in protein. It is also great if you are doing lots of exercise as the proteins helps, build and replace muscle.
You can order it off the website above or buy it from Tesco, like myself.
normally £0.99 for 25g. (enough to fill you up for a snack)

Low calorie snack: Alpen light bar
Under 70 calories and perfect for those in between meal snacks. Although they don't fill you up as much, eat them slowly with a glass of water and the effect is better. These can be found online or buy them from Tesco.
£2.79 for 6 bars, They come in three flavours.