So I've made some sims and I want to share them with friends. The thing is when I export a sim, it reverts to default stuff on their computer. How can I find out what custom content I've been using so I can share that with my friends or is there a way to bundle CC with sims?

If it's sims3pack content, it will usually package with the sim if you're sharing the sim as a sims3pack. If it's package content, look at the thumbnails - many creators use custom thumbnails with their names on, or use a particular style that's easily recognisable (e.g. there's one creator who always makes her eyebrows pink for thumbnails so you know they're hers). Beyond that, look at whichever folder is relevant (for example your accessories folder, makeup folder etc.) and figure it out by a process of elimination.

Also be aware that custom skins and hairs sometimes revert to EA defaults even if the downloader does have them.