Is there point in preparing for a game against a GM?

I am going to play in an OTB tournament tomorrow, and most likely I will have to play against a GM in the first round, as I am fortunate/unfortunate enough to be on top of the second half of the field in a swiss system.

How would you approach such an encounter? Is there a point in going through the openings of my likely opponent(s) or would that be just a waste of time?

You are going to play a game of chess no matter how strong your opponent is, not an opening only.

And anyway that grandmaster probably has a many-yeared headstart when it comes to studying chess and playing it, both qualitatively and quantitatively. So no, preparation is futile, in that sense. Just enjoy the game and after you've lost, politely ask where he/she thinks you went wrong. Enjoy it, be exited you are playing someone that strong, take no stress whatsoever or you'll play under your own level

Thanks for the advice. Sounds like the right approach. :-)

No prob. I might add maybe do some 30mins of tactical training(preferably material wins instead of mates) the same morning, just to get your brain juices running. Have a latte before the game and eat a chocolate bar during it. Not so much more one can do. GM'S are GM's for a reason. But still, I'd say it's important to play your own game, your moves and your own style. Pay attention and give it your best. But don't stress!

Play the Grob!  Just kidding. 

I wish you the best!

Offer a draw every second move. That should annoy them enough to cause some inaccurate moves. 

Seriously though, play the most drawish opening you know, avoid complications, and exchange down to a (hopefully) drawn ending. 

Be grateful for the opportunity to play a GM and give it your best shot

Play crazy. You are most likely going to lose, so prepare a strong computer line that is very, very complex, look over some of Alphazeros games for ideas, and eat some chocolate.

The only way to win against a GM is by bribe. Or by physical threat. Choose the former. Even if the GM had a terrible hangover or indigestion, no chance of winning.