Mountain bike to gravel bike conversion?

I'm taking this bike on a 270km 3 day trip soon which will be my first bikepacking trip. I want to do it as cost effective as possible.

Can anyone tell me what modifications I need to make to the bike and maybe even suggest some essential bits of gear I may be unaware of?

Many thanks.

I'm taking this bike on a 270km 3 day trip soon which will be my first bikepacking trip. I want to do it as cost effective as possible.

Can anyone tell me what modifications I need to make to the bike and maybe even suggest some essential bits of gear I may be unaware of?

Many thanks.