What kind of bike do you ride?
All I really need is my Visa, CAA and travel medical insurance.
That said I tend to bring my top box for an overnight trips and my side cases as well for a multi-day trip. If I am staying in a motel I can pack much less than if I am camping without needing the tent, stove, fuel, pillow, sleeping bag and air mattress.
I usually bring clothes that pack small and dry quickly if I need to wash them on the road. Assuming a 2 night/3day trip, I would bring 3x socks, 3x underwear, 3x t-shirts, 2x long sleeve shirts, 2x shorts or jeans, casual footwear, rain gear, extra pair of motorcycle gloves, sunglasses, hat, bug spray, first aid kit, headlamp, zip ties, duct tape, small vice grips and chain lube. I bring a small towel for my face or campground shower. I also keep a damp towel (in a zip lock bag) to wipe my windscreen or helmet visor.
I bring electronics: phone, GPS, camera, mp3 player, GoPro and all the chargers or cords that go with them, since I can charge anything I need from the outlets on my bike. Even though I tend to plot my routes beforehand in my GPS, I also bring paper maps in case the GPS fails.
I usually travel with snacks - trail mix, fruit, cliff bars, etc. I ride with a hydration knapsack that holds 2L of water.
I would suggest packing what you think you need for a ride and then heading out for a test or overnight trip. You will slowly find out exactly what works for you as it is different for everyone. If you plan on camping, doing a test run also helps to be able to figure out the easiest way to pack/unpack.