Not sure what exactly we would be trading. We’ve got raw materials up the wazoo right here in our own solar system. If it’s some exotic technology, then the information to replicate that could just be transmitted at the speed of light.
We’ve already beamed out all our best culture via radio & TV, so I’m not sure what they’d want from us (besides a “To Serve Man” scenario)
Bitcoins.
Herbs and spices that contain, say, fountain-of-youth compounds we can’t synthesize?