somehow, that "today is vet day". Sigh. My process:
0. Make sure there is no trouble he can cause in the bathroom if he gets away from you. (Breakables put away)
1. Prep soft-sided carrier in the bathroom when he isn't around to notice.
2. Close bathroom door.
3. Stealthily locate cat. Best case, he is sleeping somewhere and hasn't noticed my preparations.
4. Don the thickest sweatshirt I have (to protect skin from claws).
5. Double-check all is prepared.
6. Pick up kitty, hugging and smooching as if it is any other day. (But, by now he KNOWS. Even if steps 1-5 weren't done, he KNOWS. In all other prior methods of getting him into the carrier, he KNEW. Hence this process.)
7. Move quickly but calmly to bathroom and close door ASAP. Now if there is a struggle, at least he is enclosed and not hiding under the bed.
8. Set kitty in the carrier and zip with one hand while the other is (attempting to) controlling him and keep him in the carrier. If he gets out, at least he is enclosed in the bathroom and there's nothing to break, so you can attempt this step as many times as needed.
9. Slide treat into the carrier. (Not that it ever helped much with my kitty).
For any who think above steps are likely "traumatizing" on their own, trust me, I tried every other suggestion listed by others here and this was ultimately the only way I could ever be sure to get him into a carrier. And after the vet visit he went back to normal pretty quickly. Amazing how a cat with an apparently very short memory had "vet day radar" like no other.