Eggs. In recipes, mix together 1 teaspoon baking powder, 1 tablespoon water, and 1 tablespoon white vinegar to replace one egg.
Milk. Most nondairy milks can be used in recipes calling for cow's milk. Hazelnut and oat milks taste especially good in pancakes and muffins. Be aware that many "milks" have a high sugar content.
Nuts. Try pumpkin seeds and sunflower seeds; these are not from the nut or legume family but offer many nutlike attributes.
Wheat. Because wheat gluten is the source of bread's comforting texture, it's the most challenging ingredient to emulate. To replace a cup of wheat flour, mix 1 teaspoon xantham gum (available in health food stores) with 1 cup of alternative flour, such as brown rice flour, garbanzo flour, quinoa flour, or buckwheat flour. Chestnut flour works well in cakelike recipes.