The answer depends on what kind of key material and applications you use. Sadly there is no one size fits all system.

https://www.opensc-project.org/opensc/wiki/OverView

this would probably be the place to start, at least to figure out which type of card you'd want. The main choices are a) support pgp and ssh b) support x.509 certificate based signing c) support time or use type tokens (like smartphone 2 factor apps) or d) some non standardized system running custom code on a tiny jvm inside the card.

a) would be what you'd want in the context of this conversation, but b) is much more supported and has a wider set of use cases.

In most cases it amounts to making sure you buy the right card & reader, plugging it in, and compiling the opensc and related packages

OS X has smart card support for FileVault 1 but not FileVault 2. It only includes enough drivers to support US DoD CAC cards, and other NATO countries that have standardized on our stuff.