Standard voicepack is 3 files: .int, .uax, .u but after awhile some people started ditching the .uax and shoving all the sound files directly into the .u file. That said, if you're gonna go with stuff you have on your own system that's not readily availble to others (stuff you collected, not stuff you made) it can be hard to tell which voicepacks require what files.
There's probably an app for that.
papercoffee asked what voicepacks I have the other day, so here's a quick list:





I may have more, specific to certain models, but I think this is most of them.