Returning to the original question (I am sure it is too late for the OP but may be useful for someone else), if you are buying food whilst you are out and about to eat there and then or on a train journey, what low carb options are available?
That means, you have no time to prepare yourself a salad or buy wraps from the internet or ... All you have is an average supermarket "sandwich" option.
My suggestions are
- cooked sausages or something like pepparami
- olives
- nuts
- salad
- crustless quiche (you can leave most of the pasty if the crustless is not available)