So I've seen a provider and she wanted me to bring White wine the next time I see her.  How cheap do you guys go when it comes to buying wine for providers during a session?  Also, besides a wine opener, should I bring wine glasses our use what she got in the incall hotel?  I know not to bring box wine of course but wondered what the cost of wine is considered good without shelling to much for it.  Last, how do you guys carry the stuff to the incall location?  Don't want to make it obvious why I'm there to a desk clerk.

I was going to start with a joke about wine-in-a-box but you beat me to it. So I'll cut straight to the myth that the best wines only use cork closures. Not any more. Screw cap closures are now used on premium wines. So, you can skip the cork screw.  http://winefolly.com/tutorial/corks-vs-screw-caps/
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You can bring the wine in a bota (a wineskin made from goat bladders). You squirt some into her mouth and then she squirts some into your mouth. I'M TALKING ABOUT THE WINE! Other oral fluid exchange can come later. Modern botas use plastic closures.  With a bota, you don't need a corkscrew or any glasses.
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Sneaking a bottle of wine past the desk clerk isn't a problem. I just hide it in the hollow of my peg leg. But seriously, are you visiting someone at a hotel or at a convent? Just put it in your briefcase, backpack, or liquor store shopping bag. If you're really paranoid, but it in a Walmart bag.

http://www.delish.com/food-news/news/a53125/trader-joes-charles-shaw-two-buck-chuck/

Go for a good $20 bottle of Chardonnay, or a Riesling.   Gals seem to like those best.   They should be kept chilled, so if you have a cooler, use that.   If not, then I suppose you could use the ice bucket in the room, but it will need around 30 minutes to chill.

It could mean any number of things, such as an anniversary. Most packages are not going to make the front deskperson suspicious.

Same message, w/o the lighthearted banter.

A couple of things to add to your good advice. The younger the lady, "most likely" the sweeter the wine she will like. IOW for an under 21 girl go with something like a Pinot Grigio. 21-25 your Riesling is fine, 26-30 maybe a Sauvignon Blanc, and for the older crowd a decent Chardonnay.  

This guy IS 2 buck chuck..

to a session, I have purchased wine ranging from $20-$75. Most providers haven't noticed any difference. I've brought the more expensive stuff mainly because I enjoyed it and sometimes I just don't want to bring the cheap stuff because I just can't drink it. I've run into your issue of how to store the wine that I bring to an incall date. Since I don't like to bring a backpack or briefcase into a session and I don't want to draw extra attention with a wine bag, I have brought the wine bottle into the hotel  with either a grocery bag or small beach bag. I like the beach bag/grocery bag because people can't see what generally is in the bag. As far as glasses, I use the hotel glasses even if they are not wine glasses. I also ask my provider to have a corkscrew or wine opener available for our session. Just one less thing to worry about forgetting. I hope this helps.

...and ask the professional employed within for their advice. Twist-offs are a good idea and most definitely take a couple of *good* acrylic wine glasses (run about $4 each). I say this as a wine pro who's been in the biz for a few years and usually take wine IF the provider is into it.

Providing alcohol for a person under 21?

would always send me a text to ensure that I didn't forget to bring a nice bottle of wine.  Fortunately, I always have several bottles of wine readily available because I receive them as gifts and I'm not a heavy consumer of alcohol.  But if I had to purchase a bottle I would and didn't want to spend a lot of money, I would buy a bottle of Chardonnay or Moscato.  Keep in mind that, generally speaking, the expectation is that white wine is chilled.  I wouldn't bring glasses.  I would bring a wine opener - and although this should go without saying - I would familiarize myself with the wine opener (if it was one that I just purchased) before the session.  Sometimes they could be a little tricky.  A grocery bag should be fine.  

It's wine flavored Kool-Aid with a little bit of alcohol thrown in. lol

to serve Prosecco in the summertime. You can get a bottle for $10-20 from any liquor store. It's light and bubbly, not too sweet, also not too strongly alcoholic. No bottle opener needed.

what kind of wine she enjoys. Once you have decided on the type of wine, then go to the wine store as has been suggested and ask for assistance if you are not a knowledgeable wine drinker. The advantage of red wine over white is you don't need to chill the wine. In the past I have asked providers to supply the wine glasses if I was unable to do so (inquiring eyes). Hotel glasses can be used in a pinch.

Glasses and wine opener in my "ho" bag. Same as deodorant & soap for men.