It all come down to choices (and the fact we tend to get very anal with our diets).
1. If you can plan ahead, pack your meals. Here Miss24K is right (as she usually is)
2. If you get caught with your pants down, you have several choices: have some protein powder in your car or locker or a bar (God forbif what you choose, some bars are really shitty) or go for the least-damage approach, which seems to be what you are doing.
My feeling is that eating a relatively-safe meal like the turkey sammich is better, in any case, than skipping the meal altogether (remember you need to eat to lose weight), so as long as it's not a constant ocurrence (i.e EVERY WEEK) you should be OK.
Then again, if you get complacent and start noticing the weight is not going anywhere, you need to tighten that diet down