I used to freeze trying to figure out what to perform. (I have a big binder full of songs). So now I pick a few prior to the session and practice those, put them in the front of the binder and just go through them one by one. Sometimes I do seek for and perform other songs that seem to go more with the flow of the session.

I only started doing this a couple of years ago. I have to say now I am much more relaxed in sessions where I am known and know others. I have seen those I know to be perfectionists and those good on a professional level make mistakes and how they recover. I have seen how those I know to be nervous neophytes like me cope. All good stuff. Plates for my mental armour.

Don't be afraid to laugh at yourself.
I discovered that if I flub in mid performance, when I chuckle at my foible, I relax a bit and the rest comes much easier. A finger stumble over guitar strings can be covered with "Who put those notes in there?" I misplaced verse in song with " I swear that verse wasn't there yesterday." All of which puts a different spin on the mistake. Makes it part of the entertainment. I have trouble with songs in which I must count. Like Children Go Where I Send Thee. I start this song with the disclaimer that I am numerically challenged and will need help to stay on track.

If you can get out a good guffaw before you start it may go a long way to dispelling that initial fear.
I understand a number of performers start by telling some little funny story, providing a disclaimer or engage in self-deprecating humour.

You are doing this for fun after all and not some masochistic self-torture. I hope. Good thing to remember is to do it so you enjoy it. If you are enjoying it, people will remember that and not the mistakes.

Having said all that, this Sunday will be the first time I accompany my singing with guitar. Never played in front of people (my mom and kids don't count as people) before. We shall just have to see how it goes.

Good luck to the both of us.