Minutes and days are kept on a computer at the network ... unless it's a TracFone phone. In that case, you might wipe the minutes and time - it depends on the phone. (Older TracFone phones keep that data in the phone, and on some of them it gets lost if you reset. They've stopped doing that now, so even if you brought your own phone to TracFone you wouldn't lose any minutes or days.)
Contacts that were entered as Google contacts (not Device or Phone contacts) are synced to your Google account. Emails are kept on the server for an IMAP account. Everything else is lost.
See
Backing up an Android Device and make sure you always keep a backup of anything important.