Playing one guitar through two or more amps... would the signal get weakened or muddied at all? Is it possible to get some kind of "signal booster" to give it needed oomph, if it is needed?

Also, I could use a nice short "shopping list" of gizmoes I would need to play one guitar through two amps. I'm also wondering if it's possible to get all that needed stuff in one store. I'm still quite unclear as to what it is that does the job, as I'm a moron when it comes to recognizing gadget names.