Hi Ellie, I find the shakes really filling myself, they are great blended up with ice as well.
Snack wise I stick to 3 ~100 calories, aim for 300 cals of snacks a day. There is a thread with lots of 100 cal snack ideas on here which is worth looking at. You don't have yp have 3 100 calorie snacks though, you can have one 300 if you want etc.
Obviously it is better if you're having fruit and stuff as your snacks, but you can have anything you want - personally I tend to have unhealthy snacks but I stick to the diet this way. I recommend trying to find stuff that fills you up!