I used to feel a lot of pressure to run home at lunch to prepare a meal for my elderly mom until it dawned on me that I really could prepare food ahead of time for her. I'm passing on some tips I've discovered in the 2 years since Mom came to live with me in the hopes that the ideas might help you too.
Preparing lunches for the elderly doesn't have to be complicated, just might take a bit of creativity. One thing my Mom and I have found to be helpful is that I always leave her lunch in the refrigerator in the same spot; in or case, on the top left shelf - this way, she doesn't need to hunt around the 'fridge. I bundle up whatever is being served on a paper plate (easy for the microwave and cleanup) and cover with Saran Wrap.
Use leftovers from dinner for tasty lunches - more than once, a smaller portion from dinner has ended up on her lunch platter. A small slice of meatloaf with a side of potatoes and a roll fill her up quite nicely.
Stock the house with easy snacks - We always keep single serving applesauce and fruits in the pantry, along with single serving potato chips/fritos, etc. Crackers and cheese are another easy, light snack with my mom enjoys.
If your elderly loved one likes meal supplements (such as Ensure), make sure to loosen the lid and leave one in the refrigerator. There's not many things more frustrating to an elderly person than to not be able to loosen a top themselves.
I tend not to use mayonnaise in luncheon meals as I just don't trust that Mom might not snack on lunch for quite a while instead of gulping it down like I would. Use mustard just to be safe.