Ah, we have a cupboard full of the buggers and 2 that roll around in the car.
At one point we had 11, but we sometimes leave them at parties etc. They are good to fill with homebrew from the keggerator, and we usually leave some beer with the hosts as thanks. They usually all return to us over time, as people drop in.
They cost about $4 here at most breweries.
We even have a padded insulated growler holder with shoulder strap. Great for music festivals.
If we stop in at a brewery the 2 in the car are so we each get to chose a beer to take home.
But California is a PITA. The state law is that a brewery is only able to refill glassware purchased from them. So we own no growlers from out there.
Out here, and Arizona, Colorado and Utah at least, breweries will refill whatever growler, and sometimes slap their own sticker on. See the second growler.