Can I just buy mobile data?

Excuse me, I'm a bit confused about something. I was wondering, is it possible to simply purchase mobile data without having to sign up for a full-fledged mobile plan? I'm not really interested in all the other services that come with it, just the data itself. Is there a way to do that, or do I have to go through the whole process of subscribing to a mobile plan? I'd really appreciate it if you could clarify this for me.