Hard to tell without knowing what breads you can eat, if any. I usually take some rye bread and some pumpernickel. I like black forest smoked ham, havarti cheese, garlic sausage, pepper salami and smoked salmon with either cream cheese or dill sauce. In the box I always have things like pickled cucumber, hot wax peppers, lots of cherry tomatoesand maybe a small packet of pork scratchings. Sometimes a pear or apple. I usually like to have something warm so I have a flask of soup. The Maggi packet soup range are tasty and tend to be low carb, even the ones with noodles.
Other nice sliced cheeses are the dutch varieties, edam, maasdam, gouda etc and then appenzeller, jarlsberg, emmenthaler. There's a decent variety there that won't fall to pieces.
I also go to a farmers market every couple of weeks where a butcher always has very good quality roat pork, roast ham, roast beef and tongue. They all taste good on rye bread.
If you take some pickled onion in a separate container and maybe a small bottle of tobasco sauce which you can use on some meats and maybe in some soups, even a small bottle of worcestershire sauce, you can make a nice meal.
The main thing is to have pots and containers and a flask.
Oh, and, a bottle of something to drink or flask of tea.
