As I wrote above -- my wife and I have chosen to eat a plant-based diet but we grew up eating meat and dairy, in the same US society everyone else around us did. We have learned that it is healthier, and the change was a deliberate choice. We know we're on the "fringe" and it's our problem to figure out how to fit in socially and cope with selection availability. You're in the mainstream and don't need to make any apologies for your food preferences. He expects that.

My wife and I will have a bit of food now and then that doesn't conform to our ideals, and sometimes he might too.He may or may not be stringent.

What I do think you should do is respect his choices (it sounds like you do) and don't resent him for it. (Dan y seems to have a problem with that and I think he's taking a wrong turn). Especially since your son's future father in law has had serious medical issues. Speak with him and accommodate him to the best of your abilities. If you tell him you're not used to stocking the fishing camp for his diet, he will probably appreciate it if you ask if he'd like to bring things he likes, or (if he's flying in) offer to take him food shopping when he arrives so that he can buy things he prefers. If you don't have a "Whole Foods" or Trader Joe's type market nearby, the largest supermarkets all have a "healthy foods" section where he will find things he wants.

Easy suggestions include salads, which can include chick peas, olives, sunflower seeds, avocado, nuts, etc. You can make a fantastic 3-bean chili using all canned beans and ingredients. Fresh vegetables can be roasted or grilled, and grains can be seasoned in various ways and mixed with veggies. This is tonight's dinner (faro and brown rice seasoned with vegetable broth, covered with a variety of roasted veggies, pine nuts and pan fried onions, and we also had a salad as a side dish).