I personally savor my 500 calories and I would never waste it on popcorn (but that's me). I'd opt for a protein instead (more filling and no impact on the blood sugar). If I don't do protein, I do vegetables and fats (healthy fats). Again, personal perference, but my theroy if I'm going low cal, I might as well make it packed with nutrients.
this damn tracker below hasn't been right in months! My current weight is 139!