As stated earlier, you will never be asked for it and if you try to use it, they won't accept it but it doesn't hurt to have it.
More importantly is having multiple copies of your state drivers license and making sure it is designated for riding a motorcycle. I won't debate legalities but if you can get multiple real licenses, do it. Probably this involves losing one. That license will no longer be valid in the states but is wonderful for the road. Make really good copies of your license to use for the cops in CA. Never hand them your real one and when they ask if this is original, say yes.
It is now possible to get both a passport and the passport card. The passport card is usable as identification while your passport is somewhere safe. Get both. Also, it is great to have extra pages in your passport. If you get a new passport, ask for extra pages, they are free. If you get pages sewn in while you are in a major city abroad, they are free. If you get them for your existing passport in the states, they cost a lot. Running out of pages sucks. On a dirt bike you can cross the Argentina/Chile border enough times on dirt passes (the best) to fill up your passport (done that).