In the past I cooked myself into a corner when I realized mid-recipe that I didn't have any lemons or lemon juice available. Nor did I have any limes.
I can't remember the exact recipe, but I believe it was some baked fish dish. What are some possible substitutes for lemon juice in this application? I ended up using a dash of apple cider vinegar. It didn't turn out bad, it just was distinctly not lemon.