===== Answer =====

You can get 121 (or 122 if you cheat a bit)

Start by purchasing 61 bottles. Drink all of those and trade in 60 bottles to get 30 full bottles. Drink those and trade them in to get 15 more bottles. Drink those, then trade in these 15 plus the one we have left over to get 8 more. These give us 4 more, which give us 2 more which give us 1 more. Sum all of these up and we get 121 full bottles with 1 empty. If we borrow one more empty bottle from a friend we can get one more full bottle, drink it, and give the empty bottle back to our friend.