I've driven two hours without the reel I needed. Twice (!!) in the past two years I've hit the river without a fly rod. Both of those times were with my kayak, and both times experimenting with "solo shuttling", so, in my defense, I was pretty preoccupied, but even so...duh.
I don't know how many times I've tied flies to fish with the next day, then left them on the tying bench, or somewhere on the path from the tying bench to the car. Usually the cat finds them, and that's that. Fortunately, she's very adept at shredding them without getting the hooks in her mouth, and even more fortunately, they're all barbless hooks.
I've gotten better in recent years, since I built a storage drawer that fits in the back of my SUV, and a lot of the gear stays in there all season long.