I'm new at this gig too, but i think i can give ya a few tips here.... If you have a freezer you can easily sort yourself out some super meals on the weekend, freeze them, then before work throw em in the fridge to thaw. When you get home you will have tasty, homemade clean food ready to be heated up, toss up a salad and presto!
Soups work fabulously, i've also frozen cooked chicken and ham... i haven't frozen cooked beef but i'm sure you could no problem. if you divide them into individual ziploc baggies you should be well and sorted!
Hopes this helps some :-)