Wife and I started  ketogenic/ low carb high fat diet about 5 months ago. What works well for us while traveling is boiled eggs, cheese sticks, Iowa Smokehouse meat sticks, radishes, and cherry tomatoes, dill pickles, salt and pepper shaker. Smoked salmon or summer sausage too. We dont need to eat breakfast any more (not hungry), light lunch of some of the above, then main meal at dinner.

I remember as a kid in the summer my dad's brown paper bag lunch when he left in the morning for a day in the field was a scrambled egg sandwich on white bread, a big fresh garden tomatoe, and a salt shaker.

Eggs are hard to beat. Got about everything you need in them. An Instapot (small modern pressure cooker) boils eggs wonderfully where the shell peels off in a snap.

John