If it was me that you were leaving the food for, I'd be perfectly happy if you left me with some cheese, a few sticks of washed celery and some of my favourite cakes.
Alternatively, any variations around a 'ploughman's lunch' e.g. an individual pork pie, some pickle, possibly some cheese and a bit of salad.
With reference to salad, many older people tend to think of 'salad' as the way it was when I was a child. i.e. lettuce, tomato and cucumber. Of course, all of the big supermarkets now sell a wide range of pasta and rice-based salads, so there's no need for a frequent salad-based diet to become boring.
What to put with those various types of salad? Possibly cheddar cheese? Blue cheese? Slicing pies (i.e. those big pies they have on supermarket deli counters where you just buy a slice)? Corned beef? Luncheon meat? Roast pork or chicken slices (possibly those with stuffing in the middle)? A cooked chicken leg or breast? Canned salmon (or fresh salmon you've cooked yourself)? Smoked mackerel? Canned sardines or pilchards? Quiche? Boiled eggs? Scotch eggs? Smoked salmon and/or cottage cheese?
OK, I have to admit that there's nothing particularly original in my list but I hope that I might have given you a few ideas.
Chris