Are Wasa crispbreads low carb enough? I like this variety. It is a diet food that I like to eat.
https://www.wasa.com/en-us/products/sourdough/
I put tuna down up above. What about canned shrimp?
I bet with a few slices of egg and some shrimp and a sprig of dill on a Wasa, it might make a sort of Scandinavian snack. Also could consider smoked salmon. How about mini salmon patties or crabcakes with minimal/carb-free binders?
The South Beach Diet used lettuce leaves instead of bread. That's a possibility if you find acceptable fillings.