If you could figure out the distribution of universes, somehow, and figure out the distribution intelligences across them to a high enough fidelity to predict their actions (for example, by crunching numbers with a star-sized-computer, predicting what modal source code of some universe-spanning AI in a parallel universe looks like, and running it), you could in principle bargain in a cross-universe manner that leads to both parties/universes gaining value. Say you highly value diamond, and want to turn all matter in your lightcone to diamond; you've got 99% of it, but the last 1% is extremely expensive. Your counterparty values happy sentient life, and has dismantled 99% of the stars in their light-cone to make very long-lasting artificial habitable worlds, but the last 1% is the hardest to use- but would be easier to turn into diamonds than your last 1% of usable matter, and your last 1% of usable matter is easier to turn into living things than diamond. If you could somehow both predict with high confidence that a universe containing your counterparty exists, you could both gain value by using that last 1% to help the other, in a prisoner's dilemna sort-of-way.

(One possible avenue against defection is that if I can simulate you well enough, I know by definition whether you'll defect or not.)

This whole process is called 'timeless acausal trade', and it's pretty interesting.