I wish there were more "absolute" rules. There are so many dietary exceptions. Here are a few I live by to manage Crohn's.
Water: Probably the #1 most important thing for Crohn's patients to manage is water consumption. Bottled water whenever possible. More specifically, the more alkaline the better. Tap water, unless you live in the mountains, is commonly bad on the digestive tract.
Fried food: Generally "bad", but food fried with certain oils seems to be okay. The oil needs to be fresh. Fried food from fast food chains is always "bad".
Sugars: Complex sugars are "bad". Monosaccharide sugars, found in fruits or honey, are okay.
Vegetables: "Good" when steamed. But undigested raw veggies increases risk of triggering an auto-immune response. I eat small salads... ideally chef salads with some protein (ham/bacon/turkey).
Fruits: Similar to veggies, only small portions. Don't let roughage linger in digestive system too long.
Dark Chocolate: 80%+ cocoa in moderation tends to be okay. The endorphin rush is a plus and a good substitute for coffee.
Popcorn: Definitely off limits. Auto-immune response triggers when the body detects undigested kernels.
Dairy: Odd mix. Milk is extremely "bad". Won't even touch it. So is milk chocolate. Eggs are okay if used in cooking, but I avoid eating plain eggs for breakfast. Butter and many gourmet cheeses are fine (processed cheese is "bad").
Coffee: I drink a lot of coffee. Probably too much. The water, beans, and preparation process all contribute to coffee being "good" for Crohn's. Coffee becomes "bad" if there are any additives, such as dairy or sugar. Not even dairy substitutes, like soy, can be added.
Meats: Okay in moderation, but lately I've been cutting back on red meats after learning more about increased risk of colon cancer in Crohn's patients. High quality beef burgers and fish are common staples.
Alcohol: I abstained from drinking for many years when first diagnosed with Crohn's, but was pleasantly surprised to discover that I could introduce many "top shelf" brands in moderation without any real symptoms. I've learned a lot about the distillation process of wines and spirits as a result. There are such things as "good" and "bad" alcohol.
Craft Beer: Similar to above, there are "good" and "bad" beer yeasts and fermentation processes. It's very hit or miss, but when I discover a craft beer that "works" with my digestive system, I stick with it. Lagunitas is an example of a beer that happens to be "good" with my gut bacteria.