Custom functions. Where to put them?

[eluser]callumd[/eluser]
Hi There,

I have some custom functions that I want my CodeIgniter app to use. Where should I put them?

Should I create a new folder and put them in there? If so, what's the best way to "include" them in the controllers/classes that need them?

CodeIgniter doesn't seem to enforce any way of doing it.. so perhaps what I'm really asking for is, what is considered "best practise"?

Thanks.