So what is everyone's choice of a bike lock and how to you carry it with you? I'd like to get one that will hold up and be easy to carry.

I have a cheap cable and combination padlock which I carry on the rear rack with shock chords if I'm going to need it.
It keeps people from riding off, if a bike thief shows up they'll have the tools to cut most anything. The more you spend the more time it will take them.

Don't mean to hijack your thread but I saw this today...speaking of locks:

Bike Thieves Get Pranked in This Hilarious Video | Bicycling

I've seen that. Pretty funny

OnGuard Akita 8043 7' x 10mm cable, U-Haul disc lock (leftover from a rental storage unit) with very short shackle. I coil it up and lock it under the saddle, with a Velcro strap secured to the seat post to keep it from flopping around. I doubt this rig would take more than a minute to cut through with a decent bolt cutter but I used a much lighter weight cable and lock for years and never had a theft attempt. The real trick is to find a lockup location that discourages theft.