While you are at the dollar store getting containers, consider getting an insulated bag or two to keep things hot or cold during transport. Have to pick up some of those myself, they've lately just been one-way to my son's house... I always stress that I don't want the containers back, that I buy them at the dollar store so they are one way (my mother is continually miffed that people don't return her disposable packaging...). That goes for the insulated bags, for an extra buck at a regular stop, I just pick them up on an on-going basis. You might also pick up a fun/holiday themed dish cloth or place-mat or things like that to throw in with the meals for a little fancy packaging material.
I typically only feel like cooking every couple of days so I deliberately make "2nd day meals" whether for home or for when I was working. Now that hubby is keto he also does intermittent fasting and no more packing lunches for him!
Going along with your stuffed shells and meatloaf, meatballs are great for such meals and can be done different ways, including the Swedish version when you are tired of red sauce.
One of the ladies in my sewing group is in poor health as is her husband, for days when we have group I make lunch for her to take home so her "day off" doesn't result in more work for her. She likes "big family" type meals even though it is just the two of them so I do usually make something that is suitable for a diabetic (like I am, or her husband is) as well as my keto husband, so high protein/low carb and not so much on the pasta and rice and things I love. Corned beef and cabbage went over really well. Stews, pot roast, any of the things like I do that are "low and slow" are generally appreciated by those without the health or time to watch over them. I've found some people rather contemptuous over the idea of soup for dinner, don't understand that myself because it's something I like.
What I find goes over well are the little accompaniment like some black olives or a pickle or two. For a single person on a limited income, it can seem like quite a commitment to open a big can of them, but 5-6 in a cup is a nice treat. Plus it just seems fancy to have several containers to open then just one.
Also, things as simple as a roast are rarely had by single older people. Pork roast and I keep the lunch box sized apple sauce single servings for me, usually a green vegetable like green beans or brussell sprouts. Packs up nicely.