A helmet is a must. Going from state to state, helmet laws change. It's just best to have and wear one. I like my helmet with a dark shield. I used to just wear sunglasses, and I still do fairly often, but on a long trip with just sunglasses, my face would tan all over except around my eyes. Looked kind of funny. Bad part is you have to have a clear shield for rainy weather and after dark, or park it.
If you're going to ride in the rain (best to prepare for it) you'll need a good rainsuit. I like the two piece suits. The bottom of the legs should have some straps that go under your boots to keep the legs from riding up. When the sky starts to look nasty, put the suit on. Don't wait until it starts pouring. There are some nice rainsuits with reflective stripes and whatnots, makes it easier for others to see you.
Some type of leather boot that is over the ankle for foot protection. Lace up boots are okay but be sure to tuck those laces in. They will wrap around brake pedals and gear shifters if not tucked in. Pulling up to a stop sign and falling over because you can't put your foot down, is not cool.
I like fingerless gloves, that's a personal choice, but I have a pair of gauntlets when it gets cool. On a cross country trip, you will run into some "cool" areas. Take a good jacket and layer up if necessary. A rainsuit jacket over your regular coat can really help hold body heat in. A jacket with a zip in liner can be used over a wider temperature range. I like leather but I also have a textile jacket with built in armour.
For cross country travel, you may want to consider adding a windshield to your 650. It makes a lot of difference.
