Dimensional Gate

You are just a average ordinary every day guy (or gall) when you hear a voice in your head. You spend a solid few minute thinking you are going insane but it turns out you are not. To make a long story short you where contacted by a god from another world, a world much like medieval Europe, but this god is dissatisfied with the quality of life (and maybe more importantly the offerings they where receiving) and thus decided to give you a a power. They have given you the ability to travel between the two worlds, modern day earth, and Asphel the medieval land, as well as having a small storage space that works similar to an inventory system. They are hoping that you will go and sell some of the modern products, maybe not electronics, but they want a proliferation of spices and candles (totally not because they where jealous of the offering other gods got that had spices and things). They are not able to interfere much in Asphel so other than these power all they can do is give you a document signed by some random made up bishop certifying that you are a upstanding free citizen so you won't be treated as an escaped peasant or slave. They also tell you that as long as you don't go destroying a bunch of temples they don't care what happens to the empires, even though the emperors claim to be envoys of god, they don't really care about the empires in specific.