Since you can't really cook anything (barring the use of appliances [slow cookers, toasters, George Foreman grills, hot plates, waffle irons, etc.] brought in, which I don't recommend), I'll suggest things that are cold or can be made with a coffee maker.
Instant oatmeal packets would be a good option for breakfasts, since you can get hot water from the coffee maker.
Pre-cut (or small) fruits and veggies make for good snacks.
You can probably do a similar concept as sandwiches but with other types of foods that can be served cold. Just change up the type of ingredients. Wraps would be good, as would salads, and if you don't mind cold burritos, you can always stash some tortillas, rice and beans, pre-cooked meat, sour cream, veggies, cheese, etc. in your fridge.
Salads of various types are good, either the ingredients for them or the salads themselves. Think outside of the regular green salad and into pasta or noodle salads, fruit salads, potato salads, etc.
If you feel fancy, just some bread and fruit and nice cheeses can make a good meal. Cold soups, as well. Hard boiled eggs for protein.
Instead of the typical instant ramen, try making your own cup of noodles. Bring fresh noodles (they should keep in the fridge for the few days of the con), some type of broth flavoring, and your veggies and meat.
Here's a how-to, with a few recipes. This should be a little better for you and lower in sodium than the pre-packaged instant kind.
Otherwise, google "cold lunch ideas" and see what you come up with. There are a lot of options out there!