Relatively neutral tasting salad ingredients?

My salads had always been Iceberg lettuce, tomatoes, cucumber, and avocado. The end. A lot of vegetables tastes awful to me, arugulas are bitter, celery too strong. I can eat bell pepper alone but too overpowering in a salad. Purple cabbage, tastes off. Carrots nope. My options are too limited.

Fruits have great potential too, I love adding peaches/nectarines in mine when they are in season. What are your favorite thing to throw in salads that are on the bland/sweet side?