Hugs, Carol,
I have found that if I eat out too much I gain even if I am being as careful as possible in choosing my restaurant and my food. Often there are hidden items that make it harder to stay OP. I can gain just from the extra salt and I take a diuretic! That said, make sure you drink lots of water when you are going to be eating out to help counteract the salt. Often the portion sizes are larger than you would eat at home.
You already know the butter in the onions were a problem. If you are tempted to order them next time ask what they saute them in and stay away from the saturated and transfats.
Most of the dressings are going to have sugar. Stick a small container in your purse with your favorite OP dressing. THen you can have the flavor you like. Just make sure to ask for no dressing or dressing on the side (and then pitch theirs).
Enjoy yourself at the Caribbean restaurant but try to make healthy choices. Ask questions. Check if they have a website with information on their menu. If you've never been there, call ahead and ask what they serve. I know when I am in a group I hate to delay the ordering by trying to find something to eat that is OP so I try to have some idea ahead of time. I try not to eat out for both lunch and dinner but sometimes that isn't possible. Sometimes I will try to get a little extra exercise when I've eaten out.
I do take Metamucil twice a day (breakfast and dinner). It really helps me stay regular. And it seems to do a lot to help me eat a more reasonably sized portion.