I will share drinks, or a doob, with the lady once I get there, if she is cool with that.  Many ladies are cool with having a drink or two to break the ice, but as for 420, you will have to let them make the first move...

it should not be expected to be off the clock time.  Many appreciate you bringing a bottle of wine, and many will offer you a drink.  I don't do alcohol with a date, it does not help with keeping it 'up'.

And previous posters are right, I'd be careful with the 420 offers.

Swim

If a couple of shots is what it takes to make a loose woman out of her, I'm glad to be her enabler.

In the past I have had to send guys home for smelling like weed or/and alcohol, having bloody eyes and a difficulty forming intelligent sentences and yes, showing up WITH drugs at my incall location. I was scared and just wanted them out of there.
If you want to bring something, wine is a safest choice (champagne as a close second) and if she refuses, don't push it.
Also, if you are TOFTT hen definitely do not even talk about weed. Imagine if she is LE.  What's worse? Soliciting her for prostitution or for drugs? Or BOTH? That's a dangerous game.

....have a drink with a provider.  Whether it's someone new or an old friend, it helps break the ice and make things a bit more comfortable.

Before a session, though, I limit myself to one.  Shakespeare had it best when he wrote in "Macbeth" about alcohol: "it provokes the desire, but it takes away the performance."