Let's face it, even the most prepared cooks may find themselves running low on basics like lemon juice. White vinegar is usually a fine substitute for lemon. Here are some of the cases when it works well, with considerations.
Buttermilk
Lemon juice can be added to plain milk to create an imitation buttermilk for baking or cooking. (If used for drinking, this version will not taste the same as regular buttermilk.) If you're out of lemon juice, replace it with half the amount of white vinegar. Let the milk stand for 5 to 10 minutes before adding it to a recipe.
Dressings
For making vinaigrette salad dressings, substitute half the amount of vinegar for lemon juice. Experiment with different flavored vinegars, like apple cider, red wine or rice vinegars, and adjust the ingredients to taste.
Canned Tomatoes
When canning tomatoes at home, using vinegar works, but keep in mind that it changes the flavor. Use 4 tablespoons vinegar in place of 2 tablespoons bottled lemon juice for each quart of tomatoes. Be sure to use the exact measurements in order to ensure safe acidity levels in whole, crushed or juiced tomatoes.
Meat and Vegetables
For baked or grilled meat and veggies, use twice the amount of white or apple cider vinegar for lemon juice in the marinade.