Marks have a number of low carb snacks for example , crackling, crackling crisps , chirizo crisps quite expensive but find 1/3rd of packet quite satisfying , you can also buy from Marks and other supermarkets small pieces of cheese in multipackets whilst more expensive than cutting a chunk off a bigger piece of cheese it is an easy thing to take to work . Olives if you like them are nice but a bit messy. Another thought is that Tesco for example do one boiled egg in a small plastic pot again not to everyone's taste . Mini peppers can be quite nice as well but are higher carb then the other items mentioned