There are very few calories/carbs in a stick of celery so it would be fine. However, if you are going to go off plan at all then I agree that using MFP makes a lot of sense. I did that when on the diet to make sure that I had no more than 60g of carbs in a day and to keep an eye on my overall calories. It also made me feel like I was more in control and making decisions about what to have.