If you share a large barracks style restroom with a lot of people the best time to use it is right after it’s cleaned. Plan showers, shaving etc. accordingly. The worst time to use a “mob bathroom” is right before it’s cleaned. You are better off waiting or trying to use public facilities elsewhere than using a multi-person bathroom right before it gets cleaned.
If you share a bathroom with only one or two roommates then there are at least two theories on bathroom etiquette. One is, never mess with their stuff-including their garbage. This one never works because if your roommate is exceptionally messy, soon the entire bathroom is unusable. So this theory of bathroom sharing has to be modified immediately. Okay, so enter the bathroom with rubber gloves and a mask and execute a surgical strike on whatever the previous occupant left behind.
Now as to any supplies your roommate left behind. Take the time to close them up and put them neatly out of your way. Never borrow your roommate’s toothpaste or shampoo-you don’t want to obligated or worse, fight over trivialities. Bring along that flimsy soap and that cheap shampoo that you lifted from the last hotel you stayed at and use that stuff. One thing about those hotel brand toiletries is that they are so shoddy that no one will ever try to steal them from you. Bringing in your own toilet paper seems a bit much. Rather you should try to come to an agreement that whenever the roll gets half done, whoever spots it will make return trip with a replacement roll. Since you don’t care to be stranded, make sure you always do the replacing. This brings up a basic principle of life. There are only so many arrows in the quiver. There only so many useful fights and causes. Toilet paper is not one of them. You do the resupply so that it gets done. Somebody has to be the adult. You are elected.
The second theory on bathroom etiquette is sharing everything and cleaning as you go. If you are both faithful apostles and diligent disciples, full of forbearance and forgiveness then, beloved, doubtless this will work. If you are both young and dumb and full of piss and vinegar, it’s not going to work. And even if it did work, one of you will be more popular than the other. The popular one will have friends visiting all the time. Clever friends realize: Here is a bathroom I can use and even mess up with no consequences.
Another tactic when it comes to sharing a bathroom requires bladder control and a tolerance for public restrooms. The general rule is: Never use a bathroom that you have to clean. Always use bathrooms in common areas or near classrooms, or at fast food restaurants. Yeah you run the risk of encountering nuclear waste in public facilities but at least you never have to clean it. The real problem with this strategy is that there is almost never a shower in a public bathroom. So you are reduced to washing up in a sink like a homeless wino, or contriving to play some sport that will give you access to the school gym showering facilities.