Been there done that too many times.

Likewise. It haunts me, keeps me awake at 3am wondering where the damned thing belongs. Is my bike going to crash? Or just the CVT! OMG, I gotta find out tomorrow! Maybe now!
Things I learned the hard way:
1. When disassembling a bike, whenever possible put the screw back in the hole that it came from. That way it won't be lost or forgotten.
2. If that's not possible, use baggies. Use a baggie for each major assembly (side panel screws, back wheel parts, etc.) and label each baggie with a felt pen. I know people who actually tape the baggies on the appropriate panel. Again, that way you know where all the screws are for each task, and none of them get lost or forgotten.
3. If you have a smart phone, take pictures as you go along. It's easy and it's free.
4. A service manual is really, really, really useful. So are LeDude's guides. (Thank you, LeDude, for your generous contributions. You've bailed me out more than once!)
5. Don't get lazy. I have two Burgmans and service them myself. I've had them both apart many times. A few weeks ago one was apart for its 25,000 mile overhaul, with all the tupperware off as far back as the seat to service, add dual horns and a power block to the inside the front panel, with appropriate wiring run from the battery.
I got lazy. The bike sat apart for a week waiting on parts, I had all the screws from the LH lower side panel in a metal dish and I kicked it over. It took hours of knee-grinding pain crawling over the concrete floor before I finally found them all. I put the LH tupperware back together the next morning without incident and put the rest of the bike back together the next day. Now I'm damned if I don't have an extra screw...
Regards
Scott Fraser
Calgary