I find it difficult to bring lunches to work and even more difficult to eat them once I've brought them. I much prefer eating out. But since around January, when the coworker I was eating out with joined Weight Watchers with me, I've very consistently brought and eaten lunch four days a week. (We go out one day every week.)
I try to accomplish lunches as cheaply and easily as possible. Lately I've been bringing a main dish of around 300-350 calories and a side dish of around 150-200, so that the total is around 500 calories. Sometimes I bring cheap frozen meals for the main dish (I mean the kind that are $2 each or less), and other times I cook something myself. The side dish is always some kind of a vegetable - either frozen vegetables that I put some margarine or olive oil into, or frozen vegetables that come with some kind of a sauce. (Kroger has a line of vegetables with sauce that are about 150-200 calories per box; they are $1 on sale periodically and I stock up.)
This week I cooked a very simple main dish that was less than $5 for all four servings, and that I think will be pretty tasty. It's slightly more volumetric (fewer calories per ounce) than normal frozen dinners, and about equally healthy. And it was extremely simple to prepare.
I started by preparing a box of Pasta Roni (the parmesan flavor) according to its directions. Meanwhile, I cooked 2 cups of frozen peas in another pot. When the pasta roni was cooked, I stirred in the peas, plus a cup of frozen chopped onions (I usually chop my own, but I wanted tiny pieces for this), and let it sit for a few minutes as you are supposed to. I dished it up into four two-cup disposable tuppers.
Then I took about a pound of tilapia* fillets, which we get frozen at Walmart for $2/lb in the big box, and cooked them (still frozen) in a smidgeon of water in a pan with a lid, which is how I generally handle frozen fish. When those were cooked, I put them on top of the pasta.
And that will be lunch! I have those Kroger vegetables boxes for sides. Altogether, my lunches for the week are costing me less than $9, or $2.25 per lunch, which compares very favorably even to fast food.
(* Tilapia is a great fish. The Monterey Bay Acquarium's Seafood Watch Program, which ranks various fish based on how ecologically sound they are, has tilapia in their "best" category. They are cheap and plentiful, contain no mercury, and taste just like catfish - my favorite fish - but are not fatty like catfish.)