I'll start this with my experience, and to say up till about 5 years ago, I've never had pancreas problems, meaning it always worked. As a kid, I ate poorly. Partially because of my upbringing allowed only so much money for food in the house, and partially because it was hard to keep weight on anyways with me so active. I drank a lot of soda and empty calories, and ate poorly as a result. How did this make me feel? Miserable. I grew up without all of my vitamins and such, and although I tried to drink as much whole milk as possible I would also lose weight between CF visits.
Now that I am older and much more health conscious, my life seems to be progressing along and I feel much better. I am also maintaining my weight. The secret is simply put, eating better and more frequently. My pancreas is mostly still working. I've cut out almost all processed foods out of my diet except for some CLIF bars found in a local organic store. We juice and make protein smoothies often, as well as only making food here at the apartment. I attribute most of my good eating habits to my girlfriend, who is studying to become a health coach and holistic nutritionist. She's a very firm believer that our food is our medicine. Her and I don't see eye to eye because I demand science to her ramblings and she cannot always produce that, but she has changed my habits for the better.
That being said, I've cut out most red meat, I've tried to minimalize my fat intake in an attempt to make the pancreas work less, and I've tried to maximize my fruits and veggies intake. I don't eat things that don't agree with my stomach (fatty foods, fast food, corn, etc etc etc) and we try to cook very fresh and healthy food. We try to eat simple but healthy lifestyle foods. We typically dont buy or eat things that we can't find in an organic store, and we don't make foods from boxes or warm up meals from the freezer. Our freezer is mostly empty save the occasional frozen veggie depending on what we may be fixing.
Here's what my day (almost)always consists of. At least 1 tall glass of almond milk a day (calcium). At least 2-3 Oats CLIF bars(250calories, 6g of fat, 10g of protein). At least 1-3 20g protein bar (10g of fat, 20g of protein, 400~cal iirc) (CLIF). And I eat, constantly. I am trying to get better at always eating small meals throughout the day. I try to drink at least one cup of 8oz of juice (juiced from fruits/veggies) and TRY to include either fish or chicken into at least one meal of the day to add protein. I also drink a lot of water (at least 4x 24oz blender bottle full a day).
I don't take enzymes (pancreas works for now...) and I don't take any vitamins (but could probably use more calcium and vit d). I drink probably one cup of coffee a day and usually two to three glasses of tea. Whole ingredient tea, no added preservatives.
We still eat out occasionally, but it's rare. We aren't super picky about food we eat out, but we don't go to chain restaurants.
I've been keeping up with this lifestyle of eating and drinking for roughly 2 years now and I can tell you how it's changed me. I have more energy. In the life of CF'r that's very important, to keep going. If I know I'm going to be doing something very strenous, I know I have to keep up with an even larger intake of nutrients to fuel that. It's been working out for me pretty well, I walked nearly 10 miles last Saturday.
Last thing I'll say is you need to find a balance in healthy food and food you enjoy eating, it's a balance.