jean9, I have three of your problems (Crohn's, hypothyroidism and reflux) and a few others to boot. The Crohn's and reflux should be about the same in terms of your diet and what works for one should work for the other, for the most part. So, limit fat, caffeine, spicy foods, acidic foods, greasy foods, etc.
The only diet restrictions I can even think of in regards to thyroid disease has nothing to do with the disease itself but the medication for it...don't eat grapefruits for breakfast before taking your meds, but you shouldn't have grapefruits anyway with your other problems. I've never heard of food affecting your thyroid at all, so I wouldn't worry about it in regards to your diet. Focus on what you can eat without aggrevating your Crohns and reflux.
Everyone is different as to what bothers them and what doesn't, so you will have to try different things and keep a log of what bothers you. I could never follow a typical "diet" like Adkins or South Beach because the foods they recommend hurt my stomach and the foods that don't hurt my stomach are not allowed. I think it works better to create your own diet using trial and error with healthy food choices and exercise in any way that your body will allow you to.
Crohn's Disease, Acid Reflux/Gastritis, Hashimoto's Thyroiditis, Endometriosis, Arthritis, Depression/Anxiety. Too many meds to list them all. =)