That can be a bad thing; that can be a set up for failure.
Fortunately for me, I have an office job where there is a refrigerator, microwave, toaster oven and toaster AND a small salad bar in the dining area (that I don't have to pay for). I have luxuries some do not. However, I do hit those times when my lunch is sitting on the kitchen counter and I'm a 30 minute drive away. So what do I do?
First off, in my desk I always keep non-perishables - cans of tuna, soup, canned fruit and sometimes even canned ravioli. So if I forget my lunch, I always have something to eat which means I don't get tempted with fast food and such.
Tuna is a really good staple to have whether it's in cans or a pouch. Canned salmon and chicken can work as well. These are things that you can keep in your car, desk drawer or locker. It doesn't need to be heated making it a ready to eat option. Make sure to keep a manual can opener available in the event you get the type without a tab topped lid. Go to the grocery store and walk up the canned food aisle - pick out things you can eat that you don't need to heat or you can eat cold if the need would arise. Canned fruit is another good option (make sure it is in its own juice and not a syrup). Peanut butter and crackers are good as well.
If you have access to a microwave your options grow - soups for example or just about anything you can heat up. Access to a refrigerator? Wow - you can have pretty much anything.
So look around and see what you can find so that if you have an "oops" - you don't have to worry.