I always think of it this way. If you KNOW it's a trigger food, and still is Core (such as couscous!), then logic dictates you stay away from it. I think the inverse is true as well. If it's not Core, but you know it's NOT a trigger food (and as long as it's healthy for you), I think eating it in moderation isn't a bad thing. That's the whole reason behind the weight loss/lifestyle change thing - so that you can work into something that works for you. That said, I'd keep a really close check on a non-core food, and only use it sparingly. Of course, the Core police can be all over me on this one, but oh well.
For example, I made a taco salad the other day, and crunched up a few baked tortilla chips into it. I didn't count them because I figure, they're healthy (or at least healthier than their alternative) and they are in no way a trigger for me. I've had them sitting in my pantry for over a week now and I've had a handful once.
Good luck, and that ff cream cheese on celery does sound good.
Angela