i would like to clean out my pc of unnecessary files and programs but which ones dont i need?

what are java packages? all those zip files. do i really need them?
im not sure about these: inetfuel.exe, wrapperouter.exe, runonce.exe, rnaapp

are zonemaps needed. i see a lot of them in my registry.

as long as i can start up my pc into windows and dos without any problems what can i get rid of?