Short answer results of evolution and maybe some cultural stuff.
Life on diffrent world is going to be very different, we don't know how much chemistry we will even share in common, but we do know many biological products will be unique to their worlds.
If we share some basal genetics, unlikely I admit, then all of earths genetic diversity is valuable. but even if we don't there will still be a great deal of interest in research.
Food, this depends a lot on biology if we share some basic macromolecules then foods would tradable and many would be unique to each world, milk and milk cheese are almost certainly be unique to earth. If the macromolecules are different you could even have the dieters dream, food that has pleasant tastes but due to differences in metabolic pathways have little to no caloric value.
The sky is the limit depending on how different you make them, "Oh you have to try these cow teeth and birch bark I got from earth they are amazing, so crunchy and delicious".
Flavorings and drugs, Larry Niven's draco tavern messes with the idea that one trader makes a fortune off unique flavors of liquors from different worlds. Each world has different flavors becasue they start with different things, Earth has Gin and Beer but maybe X has something that has a flavor we can't even describe becasue it is too different. Spices would be another option as would drugs, maybe riboflavin is their nicotine or their capsaicin.
Other biological products, anything biological has a chance to be unique to one planet. Earth is likely be the only world with feathers for instance, they are just too unusual of a pathway to happen a second time and there are other things that may not evolve on other worlds. Silk or wood could be unique to earth, both might be high demand products. Maybe the aliens have a life form that makes something like foam leather or natural plastic that is valuable to us but ubiquitous to them, maybe earth plants make the the best paper or really cheap ablative reentry plating(not as funny as it sounds, oak paneling is amazing reentry plating, it is just only good for one use) maybe all their animals have scales so earth leather is better for certain things or maybe strawberries are the perfect source for one of their expensive hard to synthesize cosmetics.
Pets and the like, maybe they just think rabbits are awesome or really think crickets are amazing. Exotic plants and animals have always had a market.
Novelties, humans certainly like to steal cultural artifacts from each other why not aliens, then you have cultural fads. Maybe hair is in and humans make the best wigs or the tridions really like impressionistic art, or disco, or human coins.