Put 1st aid kit in a place not locked up on your bike. Otherwise, how can someone get it for you? Also, put a sticker on it, so someone else can find it! Tool tubes work great for this!
You have an interesting point. I do carry a first aid kit in my left saddle bag. Since I have the Honda OEM bags I have yet to figure out how to attach a tool tube because they won't mount to the inside like they can on the Givi setup. I guess I just assumed the key would still be in the ignition if the bike is a mess and they can pull the key to access the saddle bag. I hope to never need it so I primarily carry it for others that don't have one. That's what I tell myself anyway.