Leftovers, yes, but here's what I do all the time for really good, delicious take to work lunching -- USE YOUR GRILL!
Now, I have a charcoal grill (Webber kettle), and it's just a waste to fire it up unless I'm going to throw a shitload of stuff on the grill. And throw a shitload of stuff on the grill I do! Go to Penzey's spices, or Trader Joe's, or Whole Foods, and get you some various spice mixtures. Then buy big packs of chicken, beef, pork, or whatever, and rub those various cuts of meats with your various spices. Grill them. Put them in a big container/platter in the fridge.
Buy some vegetables as well. I love broccoli. I buy a few huge heads, cut them up, steam them, toss with olive oil, salt and pepper, put them in a container in the fridge. Ditto for roasted veggies like brussels sprouts, cauliflower, beets, carrots, etc. Toss them in olive oil, salt and pepper, place in a roasting pan, toss them in the oven at 450F for about 40 minutes. Put in a container and refrigerate. The possibilities are endless (try spicing the veggies up as well -- I love cauliflower tossed with olive oil and curry powder, then roasted). Of grill veggies -- zucchini, squash, sweet potato, peppers, onions, etc. When you take them off the grill, put 'em in a big bowl, toss in feta/blue/goat cheese (whichever you like), a bit of balsamic vinegar, more olive oil, salt and pepper and toss. It doesn't get any better.
Make a big pot of rice. Put in container, refrigerate.
You can easily make 5 days worth of good, healthy, tasty meals in just a couple hours. Portion out a lunch in your lunch container each night before you go bed. Voila.