Nuts and beef jerky came to mind first, those have been mentioned already.
If you want fewer carbs (I don’t think you mentioned being concerned about it, but since you mention protein possibly you are?) you can try to lettuce wrap cold cuts instead of using bread. Also, pita bread, the one with the pocket, not flat bread, will be less carbs than regular bread usually. Check the packages.
Slice of pizza is the walk to work old fashioned NYC standby. A NY style that you can fold. Cheese, veggies, and meat on top. Just pat of the grease if there is any to be sure you don’t get it on you.
Hummus sandwich on multigrain bread or eat as a dip. They sell it now with pita chips and the dip in a little package.
Egg sandwich or pita. Can be egg and cheese or egg salad. If you watch your cholesterol egg whites with onions and spinach or zucchini (I love zucchini in eggs). You can add a little bit of a strong cheese like parmesian melted.
Another suggestion for low cholesterol friendly is a bean burrito type thing. More like a wrap I guess that you can carry. Beans/legumes have lots of protein. If yöu use refried beans (you don’t have to fry them in oil) the “taco” won’t fall apart as easily.
Which brings me to, I have to mention it, because I always do, if you are increasing your intake of animal protein get your cholesterol checked. Especially if cholesterol is already a problem for you. Make sure you aren’t doing more damage than good.
Lastly, don’t forget that per calorie many green veggies have more protein than meat. Here’s a link with some numbers. That info doesn’t fit your question really, because the protein is not in a small package to eat easily on the go, but I believe it is much healthier. Maybe consider it for another meal.