A: I would encourage you to do the best that you can. For example, perhaps you could order a salad with protein, and bring your own salad dressing, or ask for lemon/vinegar and olive oil instead. I would also ask for a gluten-free menu, and see if they have any completely grain-free foods on it. (For example, they may offer zucchini noodles instead of pasta noodles.)
If you make a mistake, your progress is not lost, but you may feel discomfort until the culprit food is eliminated from your body. Dairy can take up to 3 weeks or longer to clear from the body, and gluten can take up to 6 months, so you will want to be mindful of that.
That said, eating at home and cooking your own meals as much as possible, as well as paying attention to what your body is telling you through symptoms, can really go a long way.