If it's in an insulin pen you just leave the cartridge in and carry it around now

That's fantastic! The last I remember was the Humalog pen and cartridge. That was such a major advance - yep, I remember the bottle and syringe and how strict it was from time between injection and eating. But even with Humalog we had to keep it cold all the time (or at least that's what we did, necessary or not).

Oh it just works so well to put any of this into story form. It's so much easier to understand things that way and put in perspective, and fandom's just brilliant for making the world seem so much smaller :D