maaaaybe the dock (my friend is telling me to get one)

Unless you have something to replace its functionality with already, just get the dock. You are probably going to want to plug in a mouse and keyboard and monitor eventually; it's a full x86-64 linux computer with a desktop mode in addition to being a hand-held gaming console.

Personally, I usually use it more like a traditional gaming console (with my old xbox360 wireless controller plugged into the dock and hooked up to my monitor) -- that I can pick up and take with me occasionally -- but have written code on it and installed mods/patches that have to be copied into specific parts of a game's folder and such. Just being able to use it like a regular computer is nice.

I thought the case it came with was fine personally, but I've only traveled with it a little bit.