You can subsitute any or all of these ingredients. The focus here is having variety. Different textures and flavors to your greens. Boston lettuce is soft and buttery, it pairs wonderfully with goat cheese instead of feta. Instead of chicken & bacon for your protein you might try pumpkin seeds, crushed walnuts, roasted chickpeas, slivered almonds, tortilla strips the limits are boundless. Make your salad sweet with sliced apples, figs & dried cranberries (this pairs especially well with bits of chicken salad mixed in place of a dressing! Get creative, have fun!