You can either do the research to determine what modules your applications require, or go through the list of modules, commenting out each module in turn and then testing your site to see if it still works. If it does, run it for a few days to be sure see it still works under circumstances which you probably did not test manually. Make config file backups and keep accurate and detailed notes as to which modules were removed on what dates, so that if you have a problem you can back out recent changes without having to start all over again!
Look at mod_uniqueid, mod_userdir, and the mod_proxy and mod_dav families of modules to start. Do you use SSL? Content-negotiation? If not, you can comment-out those modules.
I'd be looking for other things to optimize in addition to removing these modules -- I doubt you'll see a very dramatic runtime performance gain just from commenting-out unused modules. Script coding and database query optimizations are likely to give you more benefit.
A further thought: Just because you don't use a module today doesn't mean you won't need it. For example, mod_status is useful for debugging serious server problems, so don't remove it just to get a tiny gain.