As little as possible. I know you are the self-dependent type, so it may be hard for you to do this, but you need to do an honest evaluation of all of your gear that you would normally carry with you on a ride and remove everything you aren't likely to need. Take a tube and CO2 or a small pump in a small bag, or in your jersey pocket if you can. Remove all other racks, bags, fenders, lights (and associated mounts), etc. If you know someone with a lighter wheelset, you may want to ask to borrow it.