One of the hardest things about the Keto way of life is getting familiar with things you can and cannot eat. I cannot tell you how many posts I see daily about going out to eat and what to order. Clearly you want to go with a salad, but honestly sometimes another salad is one too many.
Obvious choices are burgers without buns, no ketchup, no noodles, nothing deep fried with breading, no tortillas, but lets dive deeper- *Side note, this is mostly for dirty/ lazy keto.*
Subway- here all you can pretty much do is another salad. Turn any of your favorite subs into a salad. Watch the tuna salad, tomatoes, onions and some the dressings.
McDonald's- Yes I know McDonald's is the least healthy thing, but truthfully, when you are in a bind you have to do what you have to do They have salads which is great- be sure to go with grilled chicken. You can do a grilled chicken sandwich with no bun or any burger with no bun.
In 'N Out- Protein style- enough said. Also stay away from the sauce and ketchup, opting for mustard.
Mexican Restaurants- Fajitas with extra guac please, hold the beans, rice and tortillas!
Italian- I avoid Italian due to the mass amounts of pasta and how much I love it. One good thing is the antipasto salad and truthfully I make that at home quite often. Also, crustless pizza is a life saver.
Japanese- I also avoid sushi restaurants, but Benihana teppanyaki grill is a great choice, just avoid the rice!
Chinese- A lot of Chinese ( and Asian) restaurants rely on cornstarch, but if you can get a side of veggies and a sauce-less protein you will be golden.
The key about eating out and being Keto is to use your brain and not fall for excuses. I am guilty of thinking, "well it is only one taco" or "I can restart tomorrw when I am not cheating", but those are lazy excuses. Keto is a lifestyle change, not a diet and the sooner you treat it as such, the sooner you will see your results.