How about some lettuce wraps? Make up some tuna mayo or anything else you like and use lettuce leaves to make a wrap. High meat cocktail sausages. Cubed chicken breast oven cooked with garlic, paprika etc
Crustless quiche, chilli and cheese poppers, crispy spiced cauli.
You could try Googling something like "Low Carb snacks" or Low Carb Buffet Food" and see what comes up. I also use a number of low carb websites. I particularly like www.ditchthecarbs.com as she also links to other low carb sites when she's doing articles on specific topics. At the moment, on her scrolling banner on her home page she has a link to "How to have a low carb party", which could be helpful.
When I do party food, I tend to go for variety so whatever people want they'll hopefully have a reasonable choice. So I make sure there are veggie options for sandwiches and quiche, for example, As well as sandwiches. I sometimes do oatcakes with toppings like cream cheese and smoked salmon. I also have a salad or two so people can fill up on that if they don't want too much carby or rich food.
Dips can be good too. You can have breadsticks or crisps to dip as well as raw veg like carrot sticks and celery, etc.
Some fresh fruit and a selection of cheeses? Strawberries and raspberries are great now,
Shush- ka- bobs with meat and veggies and of course guacamole
I agree with a 'sandwich' platter of meats and veggies. You can have rolls and lettuce leaves or remake some tuna/ chicken/ egg salad wraps.
All other ideas were good too.
Mediterranean dip is always good too