Ask 60 riders what to bring, you'll get 60 different answers.
What to bring is dependent on you. Whatever you bring it is a fact you will forget something and it is also a fact you will carry along something you don't need; that's just the way it is. The trick is to only forget those items that you can get anywhere.
There are certainly items that you do not want to forget and, if forgotten, could be a show stopper to varying degrees; meaning, at worst, you're done before you ever start or, at best, the absence will cause great discomfort or disappointment.
Valid Insurance Card
Valid Motorcycle Registration
Tire Patch Kit
What you bring along, as far as clothing and comfort items, is up to you and your preferences. Ask some and they will tell you, "...bring a tent." Ask others and they will tell you, "...don't bother bringing a tent."
Whereas wearing clothing while riding is a law in most states (go figure), wearing clean clothes while you ride is a personal decision. Don't weigh yourself down with multiple changes of clothing. Again personal preference, but for many it is more of a "t-shirt, socks, underwear" thing. Put on a clean pair of jeans and you becomes a magnet for mud, bugs and rain.
Consider it a duel with the law of chance. It's an easy bet, no matter how hard you try, you're gonna forget something. From time to time you'll win, other times... you won't.