First things first: What is the most effective way to inform your waitperson that you can't have any milk products?
If you say, "I can't have any dairy products, so tell me what I can eat," the following is likely to happen: They'll run down the list of dishes, stop on a item and say, "No, you can't have that, it has eggs in it." I usually politely explain that an egg does not come from a cow, even though they are found in the dairy section of the market. What I want to say is, "Hello! When was the last time you milked a chicken?" I swear this will happen 7 out of 10 times (or more).
If you say, "I can't have any milk products, so tell me what I can eat," the following is likely to happen: They'll recommend a dish that obviously contains cheese or a cream sauce, like Veal Parmigiana or Fettuccine Alfredo. Then you'll have to say "Um, cheese is a milk product." They'll say "Oh yeah." Or you're likely to get "This should be OK, it just has cream in it." This is less likely than them thinking an egg is a dairy product, but it happens about half the time.
Sometimes they think mayonnaise has milk in it, because it's white. (Regular Mayo has no milk in it, but some non-fat mayo may.)
No simple sentence I've ever used has ever worked. So here's what I usually say: "You'll have to help me with the menu because I can't have any milk products. That includes cheese, cream and milk, but butter and eggs are OK." (Butter contains almost no lactose, so I don't worry about that.) That usually works nine times out of ten.
What is Safe?
There's no easy answer to that. But here are some tips I've learned throughout the years.
When bread or toast is part of a meal, then rye and sourdough breads are usually safe. English muffins are usually safe too. Whole wheat bread is almost certain to contain milk, with white bread you also stand a good chance of getting milk.
Avoid scrambled eggs and mashed potatoes as these are most often made with milk.
Obviously you're going to avoid anything with cheese, cream or sour cream. Cream is often used in gravies (even brown gravies), so be careful there too.
Salads would seem safe, but I've learned to ask if they put cheese on the salad. Happens a lot. Salad dressings are tricky. I avoid anything named "creamy" like creamy Italian, although it often doesn't really have any milk products in it. Better safe than sorry. Oil and vinegar is always safe, if you don't mind it. If I want Italian dressing (my favorite) I'll order it on the side (they always put too much on anyways). Then I can decide if it looks milky before putting it on the salad. They'll often neglect to mention that it's Creamy Italian, sometimes even calling it vinaigrette. And every now and then it will contain parmesan cheese (look for little white flecks in it). Thousand Island dressing is usually safe too. But I have learned to enjoy salad without dressing. I just put on some salt and pepper. The greens are usually wet enough to hold the salt and pepper in place. It's really quite enjoyable and has a lot less calories!
Desserts are the biggest problem. It's very hard to find a dessert at a restaurant made without milk. You may be able to get some fresh berries or fruit. But don't be surprised if the waitperson only has half a good thought and says something like, "I could bring you some fresh berries and cream." Do not expect your waitperson to remember that you have LI . The person who was very conscientious about recommending a milk-free entrée may very well have forgotten about your LI by the time dessert rolls around. You can't really blame them. Once in a while you'll get a waitperson that has LI or lives with someone that does. My tips will always be more generous if the waitperson goes out of their way to help me with a food choice, and bigger still if they remember by dessert time.
Here's a general tip: Don't be afraid to make your own menu out of what you see. If there's an entrée that sounds good but the sauce has milk, see what other (milk-free) sauces might go well with it and ask if you can substitute. Or if the entrée is milk-free but comes with a side dish that is not, ask for different side dish (possibly one you see paired with a different entrée). Often restaurants are very accommodating. (This can be especially helpful in those restaurants where the menu changes daily or weekly and there's only a few menu items to choose from.)
Types of Restaurants:
Italian restaurants can be a challenge. 80% of the dishes have overt cheese. Some will have sneaky cheese, like cheese mixed in with a spaghetti sauce or minestrone soup. Then there's the cream-in-the-sauce problem with the other 20% of the dishes.
Pizza - well what can I say? Order it without cheese (but with other toppings to compensate). Learn these phrases: "Cheese is only a standard ingredient on a pizza in the US." "Almost everywhere else in the world cheese has to be ordered extra." "The original pizza had no cheese." (Remember these and use them when your friends give you a hard time.) Actually the cheese adds very little flavor to a pizza. We had been making cheese-less pizza at our house (and ordering it out) for years. One day we found some soy-based mozzarella-style slices. So we bought some (outrageously expensive) with the intent of having a pizza with "cheese" again. We discovered we liked it without better! Now when we order in pizza, we'll get half of it without cheese (my kids like the cheese - actually my son won't turn down a pizza with cheese, but he now prefers it without cheese. Besides, he says, it reheats better.), but they will also eat the cheese-less pizza without complaint (if Dad leaves them any). Recently my son's soccer team had their end-of-year pizza party and we ordered two pizzas - one with cheese and one without (the latter for me). But the kids (and not just my kids) scarfed down the cheese-less pizza before I even got any! So the bottom line is that cheese has one main function in pizza and that's to hold the other toppings in place. Here's my last pizza story: Years ago I was working in Silicon Valley and it was common for the company to feed us at night if we worked late. When we had pizza I would ask for a personal size pizza without cheese. One night the box came with a note written on top from someone who worked at the pizza place. It read, "How can you eat this?"
French restaurants: Forget it. Cream, cream and more cream. And more often than not they get snooty if you ask them to leave off the sauce or modify a dish by substituting a different sauce without milk (in the rare chance this even exists). I avoid French restaurants, but I was never a big fan of French food even when I could eat it! Here's a tip: If you want to sound hip, like you know food and possibly avoid the waitperson or chef's wrath, then say, "Could you please ask the chef to prepare this entrée with a simple demi-glacé, but made without any cream? Butter is OK, by the way."
Indian restaurants are tricky too. They use a lot of yogurt in the sauces, so ask. I'm not a big fan of Indian food, but I like the Tandoori style. If you avoid the sauces, you can eat pretty well in a Tandoori style Indian restaurant.
Chinese, Japanese, Korean and other Asian restaurants are pretty safe. Lactose intolerance runs high in the Asian population so it's not surprising that almost all of their dishes are made entirely without milk or dairy products. The exception is green tea ice cream, but I imagine that's not very traditional. Sometimes a Japanese restaurant will have milk in their salad dressing. Miso soup may look milky, but it's tofu (soy) that gives it the milky look.
Mexican restaurants are pretty limiting once you eliminate everything on the menu that comes with cheese. They tend to put the cheese on/in everything, not just the obvious things, so be sure to be very clear with your waitperson you don't want any cheese on anything. Chile Colorado or Chile Verde are usually good bets if you like them. Arroz con Pollo (rice with chicken) is also usually safe. Chicken Molé (chicken with a chile/chocolate sauce) is great if you can find it (molé sauce should be made with cacao powder and not a chocolate with milk in it). Tacos are easy to order without cheese, but beyond that, good luck. Be careful of guacamole as often it is mixed with sour cream.
Fast food is always a crap shoot, but sometimes unavoidable in our hectic lives. In the standard burger place, obviously avoid cheese on things. The buns are likely to have milk in them, but if you can tolerate some lactose you should be OK. You can assume the chicken breading contains some milk, so if they have boneless, skinless chicken breast on the menu, opt for that if you don't want a burger. Some of these places have a list of what ingredients are used in what. What really irks me about most of these places is their "Combos" and a lot of their specialty sandwiches come standard with cheese. Yes you can ask them to leave it off (one advantage is you are likely to get a freshly made sandwich), but you still have to pay for it. Some places (like Burger King) at least price all their combos without cheese. Still others (like In 'n Out Burger) actually subtract the cheese price from the product. I applaud (and patronize) these places over the others.