Twilight is very particular about her tea. So particular, in fact, that the only store anywhere near Ponyville to sell her favorite brand is a small tea shop all the way out in Canterlot. This presents a problem, of course, because she's a very busy pony, and she just doesn't have the time to head all the way out there every couple of weeks... but then, that's what #1 assistants are for, isn't it?

Sure, having to leave town so often is pretty inconvenient for Spike, but that's part of the job, and besides, the arrangement works out for both of them; Twilight gets her tea, and Spike gets some time off to visit his old friends in the city. After all, it's not like buying tea is a particularly difficult or time-consuming task. Well, not usually, at least.

(I've tossed in another story, "No One Kicks You Here, Bluenote," as a separate chapter. It's just a nasty, scrappy little thing that I put together as part of an audition and it doesn't really stand on its own, but it's tangentially related to the main story (even though it only really serves to explain a joke that didn't need to be explained) and there are some lines in it that I still kinda like.)