I've left my bike in parking lots all across the country overnight in hotels, etc. You need one thing more than any lock, a cover. Thieves go after low hanging fruit. It's not worth the effort to look under a cover 90% of the time, they just keep going. And not a full cover, but a half cover that still shows the wheels so it's obvious it's not a Harley or other high end cruiser or fancy sport bike.
I used to use a disk lock with an alarm. They are great until the wind picks up and it starts going off in the middle of the night. Or worse, the time the battery got low while I was on a trip. In the middle of the night it starts chirping, (low battery alert). I ended up taking the battery out after removing the disk lock from the bike since I didn't have the tiny allen wrench to easily replace the battery. I still have that disk lock, but never use it any more.
If someone really wan't your bike and is prepared to steal it, they will. A little liquid nitrogen and a hammer and no lock, chain or cable will survive. If it's not locked to something solid, they can just pick it up with 4 guys and toss it in a van and be gone in seconds.
Lock the forks and cover the bike. When possible park where you can see your bike at restaurants. Don't leave easy to grab items unsecured. I lock the helmet to the bike if any doubt exists with a cable lock. My panniers are locking. After that, it's up to your insurance.