You are 9 syns for a white or wheat 6" sub. Add free meats like turkey, ham or chicken, salad and avoid the cheese and dressings.
Subway give the calories for their dressings so you can use 1 syn for every 20 calories - the lowest is honey mustard at 1½ syns per serving but be aware that a serving is only about a tbsp and they can easily put on four or more times that amount. It's a very easy way to really push up the syn content.
Or they have salad bowls which would be free on EE if you have the meats mentioned above, again with no cheese or dressing.
I get a plain salad and then add my own bits and pieces eg boiled egg, quorn peppered steak (½ syn), babybel lights (HEA) and balsamic vinegar (free) - yummy!