Josh Allen's getting ready to tie the knot with Hailee Steinfeld ... but first, he's celebrating his last days as an unmarried man with some golf -- and his NFL star pals!!

The Buffalo Bills quarterback traveled to Jupiter, FL to watch a TGL event as part of his bachelor party week ... and all of his closest boys -- including Vikings signal-caller Sam Darnold and Jaguars wideout Christian Kirk -- went along with him for the ride.

The dudes took in the Atlanta Drive GC vs. Jupiter Links Golf Club tilt ... and while Tiger Woods' JLGC team -- which the guys were clearly pulling for -- lost, Allen and Co. still seemed to have a blast nonetheless.

They were featured on the match's broadcast several times ... cheering their tails off for Woods in some upper deck seats.

And, even after it ended, they got a shoutout from Billy Horschel, who teased them live on-air for rooting against his squad.

No word where the party will be next -- although there's been some speculation they moved a bit up north for a round of golf Wednesday.

As for the upcoming nuptials with Hailee, Allen proposed to her only a few months ago ... but they reportedly began finalizing wedding dates as soon as Buffalo's season ended.