I lost it twice, first when I first bought an iPhone at the Apple Store, then 2nd time was when I returned that same iPhone and got the SIM back but then misplaced it.
I have a few round camera film containers. I carry a pin to oepn the SIM tray and the SIM card in it. I also keep used to keep a SIM cutter, but these days when I travel overseas, one can easily buy nano sims.
The 2 options I've thought of are taping it, or carry an envelope. Unless I change my mind, I plan to get a local SIM on my trip next year.
Another option is to just have a second phone. Use that local, if your normal phone/plan supports Wi-Fi calling, keep your SIM in that phone and you can make calls back if necessary on Wi-Fi without roaming charges, and use the unlocked phone for local data and calls.