Yeah, the controller pack I have isn't so great. My official N64 Controller Pack went missing a long time ago, and the Performance one I'm using, unlike one that I had before, actually works, but I'm not sure if it holds as much, or more, or whatever. I do know it doesn't hold much after a save of Hexen or Mario Kart 64 TT data (which it certainly can't hold simultaneously).
So, is there a higher-capacity memory card that isn't unstable crap? If it fits in the controller without sticking out like a GBA game on a freakin' DS Lite, even better, but I can't be too picky about this.