Crisis... no lemons in the house. Don't even think about finding nice olives around. It is martini hour and you don't want to head back out... If you are really scraping the barrel you can make a twist using grapefruit (oranges seems to render a too bitter twist). Like I say, crisis. An acceptable alternative is a few slices of firm pickle, maybe something small-batchy like Moon Brine. But what is the back up plan...
A jar of commercial cornichons (gherkins) have a shelf life of over a year (hand packed containers from the deli will stay crisp for months too) so can hang around the fridge as back up. Better than just crisis material though, these are becoming my goto. I'm going to argue that this makes some regional sense; cornichon pairing w/ French vermouth just by virtue of geography -though truthfully I'm in the Churchill/light-hits-the-bottle camp of martini drinkers. Don't be shy, add a small handful of cornichons to munch on.
Bonus; you will now have an excuse to buy a pickle/gerkin/olive fork. Retractable tines or three-tined trident style or even the grabber, $5 each.