LF1 Extra Battery
Yeah no one seems to actually have it in stock, but the usual places should be getting them shortly now that the camera is shipping (I pre-ordered it at B&H and only just got it last night...). B&H allows you to pre-order an original OEM battery for $40:
Bestbatt will have a 3rd party replacement battery for $18 and an external charger for $18:
No clue whether that might arrive before the OEM battery at B&H or Adorama, worth keeping an eye on both. Another alternative, since the LF1 features in-camera charging, would be a USB battery pack or bank... It works the same way as plugging it into the wall with the stock charger (which outputs a pretty standard 5V@800mA, like a lot of smartphone chargers).
Here's an Anker battery pack that I bought over a year ago on Amazon:
It retains it's charge pretty well and seemed to have the best combination of positive reviews and a low price when I got it... Anker has a smaller/flatter model (sorta phone sized, small phone anyway) with a built in cable but you'll still need Panasonic's custom cable so that last bit isn't very helpful. You should knock off about 30% from the stated capacity to figure out how many charges you'll get out of it (due to power transfer efficiency etc). Almost of them will be good for at least two or three full charges of the small LF1 battery tho (959mAh IIRC). Useful for your phone too etc.
That one doubles as an LED flash light btw (about as bright as the tiny keychain ones). That kinda USB batteries is small enough you could even hook up the camera to the battery and slip it in a pant's pocket, effectively charging it while out and about. I do it all the time with my phone when I neglect to charge it the night before!). Might be a little clumsier with a thick camera (compared to a 9mm phone) but if your pockets aren't very roomy you can just put the camera in one pocket and run the cable to the battery in another pocket.
The stock cable that comes with the LF1 happens to be the perfect length for that too btw... It's like 2ft or 2.5ft long, just long enough to go from a few inches into my right pocket to a few inches into my left. I actually just tested this for the purpose of the post.
Just a few suggestions, hope it helps!
P.S. Just saw Anker makes a lower capacity one in the form of a cylinder (probably the size of a flashlight or a roll of candy), even that one at 2600mAh would be enough to recharge the camera twice over (or once + a 50% charge for a modem 4"+ smartphone).