If you don't have lemon juice, don't hesitate to replace it with vinegar or even some white wine. However, cut the proportions in half.
And if a recipe calls for vinegar, but you don't have any or aren't a fan of the taste, replace it with lemon juice!
If you need lemon zest but you don't have fresh lemon, go ahead and just add two teaspoons of lemon juice (even the prepared kind) or some lemon syrup.