Hi, I was a flight attendant for 19 years. In many airlines now, upgrades are authorised by systems on the ground, and priority is given to passengers of commercial importance. Flight Attendants have no authority to upgrade. Also, flight attendants have no problem sourcing their own alcohol from duty free outlets in their travels, and aren't going to be interested in yours.  

So, don't do it! I have better advice for you here: https://earthlingtravels.com/2016/09/04/how-to-score-an-airline-upgrade/

1. It's a proven fact that all air host/esses are human beings. Treating them as such will make both, them AND you feel much better all along the flight (a kind 'hello, how are you' + a smile from PASSENGER's part will work wonders).

2. A kind gesture is a kind gesture as long as it remains within reasonable proportions. Throwing a couple of wine bottles into their lap would look 'a little' weird (+ it might cost you more than the goodies you expect to buy by such a gesture...).

3. However... as it was suggested by others here... a variety of chocolates bought at duty free followed by: 'here's something to make your flight sweeter' may work wonders. Not because it's a bribe but because it is a nice, human, friendly gesture.

4. As a tour leader I find myself flying time and again with same staff. The basic idea is: 'Why don't we all make the best of this experience?'. Once you arrive to the airport with THIS attitude - the whole 'chain' will treat you MUCH nicer. Help THEM have a best shift - they'll make YOU have a best flight experience. NOBODY will abuse their position for a bottle of wine. Almost everybody will react friendly to a friendly gesture... 

Smile - the whole world will smile with you :-) Frown - and you're alone....

Well Gregg,

That's a new one on me!

In short, don't count on it.  There are several reasons I say this.

1. Although a flight attendant usually appreciates a small token gift from a passenger, there may be several problems with a gift of wine.  First, it wouldn't surprise me if most major airlines (if not all airlines, period) have some regulations in place concerning the gifts an employee may receive.  In fact, most places of business have these types of policies.  They usually focus on the value of the gift received, however.  Still, these limits are often quite low, and were also written long ago.  So, 'a couple of bottles of wine' may already exceed the allowed gift value for those employees.  In addition, seeing the primary function of a flight attendant is to ensure passenger safety, receiving a gift of an alcoholic beverage (consumed or not) may be strictly forbidden.  I'm sure that would be the case of an airline from a predominately Muslim nation; the same as a gift of cannabis would be forbidden by many national carriers, even if the flight originated where it is legal.
   
2. Another problem with bottles of wine is, there are usually more than 'a couple' flight attendants working each flight.  You'll need to know the right person to give these bottles to.  Don't make the mistake of thinking that all the flight attendants are attached at the hip; working, living, and spending all their free time together.  There is likely someone who is going to feel snubbed by being cut out of the wine loop.  This could translate into a rough time for you, as well as the person who received the wine.  Since the other flight attendants have to work with this person, their primary focus will be on their work environment, rather than pleasing you. 
   
3. Such a gift could be seen as a blatant attempt to bribe them.  Now mind you, I'm fully cognizant of the fact that that's exactly what it is.  However, such a gesture could be viewed with contempt by the flight attendant in question.  So, not only do you part with your wine, but you may have achieved the opposite desired effect.  With the increasing number of passengers being put off planes in recent years, why would you wish to immediately be viewed as a potential problem.
   
4. Finally, the fact is that upgrades are simply becoming harder and harder to come by.  There are several reasons for this.   Airlines have slashed first and business class fares, enticing more people to buy them.  Also, airlines are offering cheap last minute “buy ups” to first and business class when you buy an economy airfare.  Finally, most airlines are in the process of revamping their loyalty programs (again!).  Soon the points earned will be based not only on the number of miles flown, but on the amount spent on the tickets in question, as well as the frequency flown on a particular airline.  Now that the system will no longer be based on 'miles', but rather on 'points earned', airlines are free to arbitrarily set the number of points necessary redemption.  A number of airlines have already unrolled plans where points can be used for upgrades, rather than tickets.  This all leads to the same thing; there are going to fewer and fewer seats available to be used for upgrades.  In fact; one major carrier unveiled plans in August of this year to award only 25% of the current mile/points under this new system, when flying on a partner airline.  Their aim is to increase the their seats sold (via original booking or paid upgrade) from 31% as of 2011, to 80% as of 2018.
   

Now, I'm not saying that shouldn't make some gesture to help your cause along.  What I've found most effective (for a pleasant journey, even if there is no upgrade involved) is, when you enter the plane,

• look them in the eye,
  
• smile,
  
• and say "hello".
  
• A small box of good quality chocolates is a nice gesture which can usually be enjoyed by the entire cabin crew.
  

Many flight attendants have said to me that few things leaves them more peeved then people walking by them as if they don't exist, or aren't worth the time to acknowledge.

So, good luck, Gregg!  Let us know how you make out.

Happy Travels!

By the way, I wouldn't mind hearing from flight attendants on this issue.

My husband flies worldwide and frequently buys in duty free. He has never received an upgrade for that.

I seriously doubt it.  Bribery is typically frowned upon in the airline industry.

I'd say no. It would be nice if it was that easy though!

I always use a box of truffles (chocolate) but it hasn't worked yet. If the plane is full it is full

No chance in hell. The last person they would ever want to give an upgrade is some potential boozer, so arriving with bottles of booze is a big no no. 

Best thing is to look like someone who the other business class passengers would not mind sitting next to and some frequent flier status really helps too.