If you are selling VPS and Dedicated servers then unless you have pre configured plans then everything is added as an addon, as the buyer may just want a barebone server.
If you are selling shared and reseller plans than everything is included in the plan price
We charge for dedicated IP's. Not that dedicated IP's are really needed anymore in a shared environment. We also don't offer them publicly any more...
Apart from that, the usual things such as extra space or bandwidth. Paid SSL's from places like Comodo or the Symantec group (sometimes GlobalSign). We still get people wanting those despite Let's Encrypt and AutoSSL being offered on all of our servers.