I wish your question were an easy one to answer, but unfortunately it isn't. What one person with IBD can eat and feel fine, another IBDer might not without feeling ill. The best option is to keep a food diary - write down everything, and I mean EVERYTHING, that you eat and drink. Then write down how you feel after eating it. Do this for a minimum of 2 weeks, a month is even better, and you will be able to see which foods or drinks or gums, candies, etc. make your symptoms worse. Then, you need to stay away from those foods.
If you can be very disciplined, you might even consider doing an Elimination diet - you can read about my experience doing it either on this site - http://www.healthcentral.com/ibd/c/2623/21401/elimination-diet
or in my book, Living with IBD and IBS.
Overall, most of us find that eating whole foods, not pre-packaged or processed, to be the best way to go. Preservatives are a killer on my gut and many other IBDers. Other foods that commonly cause problems include: caffeine, sugar, high fructose corn syrup, any preservative, whole grains, acidic fruits like oranges and raw veggies, among many others.
Eat foods that you can see in their original state, and be sure to steam veggies until fork-tender.
Read through my Shareposts, try your food diary for a month, then come back and let me know if you have any other questions.
You can get through this!
This was a ridiculous answer. I didn't ask about IBD. I asked about collagenous colitis.
Do your research, CC is a part of the IBD family.
I was first diagnosed with MC/CC, then it turned into UC.