If this is an emergency, hang up and load ur 9mm. Don’t have one?, you’re SOL.
Having a 9mm choice is fine for most situations. Consider more options than 9mm though. I have 5.56 NATO options, .300 Blackout options, 12 gauge shotgun in #8, #9 shot, and 1600 fps slugs, and .458 SOCOM options too.
All of the above rifle caliber options work with ONE mil-spec lower receiver, the AR-15. All one needs to do is to push out two pins, and switch to the required upper receiver.
(I even have .22 LR options for bunny rabbits.)