No more Start-up disk space or memory... What are my options?

I have a MacBook Pro (2008) and its reached its capacity in terms of memory and start up disk space. Applications and software are unable to update. Nothing can be saved or downloaded. This has presented itself as an issue since my Mac is now quite useless to me if I can't open applications or save documents.

I don't want to delete my documents... I've already gone through and gotten rid of anything that I no longer needed.

I would like to know what my best options are...

Would it be best to get a new lap top... or an iMac...

I don't know what a Mac mini is and whether that would be relevant to my situation...