Well as you don’t want processed meat, if you have a roast during the weekend there’s nothing as good as a roast chicken, stuffing, tomato, lettuce, (English) mustard and mayo sarnie.
If you ever have roast beef, thin sliced beef (we have a meat slicer) and horseradish makes an awesome base for a sandwich filling.
Egg salad? Much maligned (one office I worked in had an unofficial ban on people eating this) but very nice. Just don’t add cress as its not the 1970’s any more.
I know its cheese but thin sliced Mozzarella you can add tomato, rocket and a little bit of olive oil…
Get some decent chutney, not the generic supermarket tasteless branstons knockoff stuff (eg apple and balsamic)
Or there’s always banana and jam 🙂