The idea behind the no "white" diet is the idea of cutting out all refinied and processed foods which do have GMOs and way too many additives; basically, he's eating clean.
Most food products that do have the white variant, such as white bread, are overly processed and highly unhealthy for you and your digestive system (here, I would consider researching what excessive processed gluten and additives can do, since that is a very long discussion otherwise.)
You can eat things that are obviously in containers. The idea is to start researching and reading all the labels of what you are actually buying. Most canned items are high in sodium and preservatives that actually go toward weight gain, even if it is a healthier selection such as navy beans. I had this misconception when I first started to try and lose weight and eat healthier. Read the label, most canned foods either have excessive sugars (which are the processed ones, such as fruit in high fructose corn syrup) or have the sodium amounts. Like most beans or vegetables in cans actually have an average serving size of 2-3.5 servings in one can and each servings size has usually at least 30% of the daily, standardized sodium amount. Be careful when reading cans and bags, etc. because the serving size often goes missed and after eating a whole can of fruit, veggies, etc. you could have maxed out one of your daily limitations already!
Organic sugar sources and organic sugar replacements are acceptable because they don't cause as much of a spike in blood sugar/glucose, but you do need to be aware of what non-organic sugar replacements may consist of: there are some pretty nasty chemicals in western foods now-a-days. I generally stick with stevia (or any other product that has been verified as organic and non-GMO.)
For your other questions,
1. There are many natural stores, but even stores like Wal-Mart generally carry more organic, natural products. I use a store called Nature's Pantry. Nothing passes that store outside of local, organic produce and every other product you could possibly imagined, so as long as its verified organic and non-GMO. As for bread, you can make your own with unbleached, unadditive flour and sweeten with honey and make light and fluffy with almond milk (I cook a lot of what I eat now.) You can also purchase bread made out of gluten-less flour, such as rice flour (although, I was not particular to the taste) or just purchase an organic bread meaning it was made from non altered wheat, etc.
2. Eating out with friends is tough. My family eats out a lot and it is still a constant struggle. Remind yourself of your goal, is the biggest motivator. Drink several glasses of water, avoid appetizers, look for more natural selections, not necessarily salads. Avoid the saturated fats! And eat slowly (hell, play with your food!) and make sure when you're about 80% full, that you stop and just drink more water.
3. I learn to look for the local, organic produce and food selections. True, it is more expensive, but my take on that is, is worth to have organ failure, cancer, etc. later in life because you simply did not want to eat better? Which is more expensive?
Food is great! Believe me! I'm American and food is my culture (as it is in almost all other cultures.) But if you love eating, then you should feel good about what you are eating. I love me some diet soda, but aspartame is not something I want to keep continually feeding my body, so I've been slowly switching over to zevia soda which is not all that bad. And organic chocolate is not really hard to find, but still, go lightly with sugar.
As recommendations, I would say try larabars (they are made out of dates, sea salt, and whatever other ingredient needed for flavor.) They are delicious and great for the digestive tract and keep you full. Well, good luck! If you have any specific questions, let me know. I was just trying to find a basis since there was so much in your post.