1 teaspoon of baking soda with 1 tablespoon of vinegar (for each egg) works well in cakes, cupcakes and quick breads. Any variety of vinegar like white distilled vinegar, apple cider vinegar, balsamic vinegar can be used, but I personally feel that apple cider vinegar does not leave any after taste/smell.
If you don't have vinegar you could substitute 2 tablespoons of lime/lemon juice for 1 tablespoon of vinegar.
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recipes using vinegar/lemon juice as egg substitute in baking recipes.