You can eat between meals but you just need to be aware of the total calories consumed.
Snack wise I have things like iced gems (per bag 98/0.8), pink 'n' white marshmallow wafers (each 50/0.1), 6 or 7 jelly babies (115/nil), very low fat crisp type things (per bag 40/0.3), crackerbread x 5...