Smoking — never, and I wouldn't recommend it to anyone. Your lungs and your
poker game will both thank you.
For me it's a glass of chilled white wine. Two maximum. And before anyone says alcohol and poker don't mix — I'd argue the right amount doesn't hurt. It takes the edge off, relaxes the overthinking, and somehow helps me make calmer decisions. The key word is two. After that you're not playing poker anymore, you're just donating chips with a smile.
I also have a habit of putting on a neutral movie in the background when playing online. Nothing too interesting — just enough noise to keep the atmosphere comfortable without stealing my focus.
The moment I start actually watching the movie instead of the table though — that's my sign the session is over. 😄