Mildly useful tip: when you take a card or battery out of your camera, leave the door open until you put it back in. That way you’ll know if you forgot to put one of them back into the camera. I do this and it’s saved me a few times.
Doesn’t that increase the chance of breaking the door? I’d say having extras is a safer choice.

Extras can be pricey. I have two kids in youth sports and shoot a few games a season to give everyone photos. Bursts on an A9II drastically increase the odds of getting some good hero shots like a ball leaving a batt or going into a glove, but it’s really easy to blow past 4k photos. Fast cards tend to be $$ :(

So anyway, I was at a game last weekend and scoping things out. I flipped the camera on and…