Children bringing such stuff to school in ‘90s would definitely have it confiscated.
Schools cracked down on the wearing of slap bracelets after hearing reports of children seriously cutting their wrists on the metal interiors.
Coed Naked T-Shirts
Some of us were old enough to get the jokes. Some of us weren't. We all understood the word "naked" though, which was enough to try to hide them underneath button up shirts.
Homemade Pen/Pencil Cannons
When we got bored in class, sometimes our thoughts turned to turning the contents of our pencil boxes into projectile weapons. Hacking a retractable pen was the best option -- they needed no additional parts to fling something across the room.
Fights over games or trading could lead to an outright ban for everyone. But some teachers were never big on the idea of tossing heavy metal slammers around in the classroom.
Tamagotchis were confiscated for being remarkably irritating beeping machines. Anyone who owned one was too busy feeding it to pay attention in class anyway.
Administrators often banned temporary tattoos as part of the dress code, perhaps because they felt they would encourage actual tattooing. Sometimes we were warned about sick individuals who used temporary tattoos to get kids high on lickable PCP.
Scary Stories to Tell in the Dark
Parents objected to reading Alvin Schwartz's terrifying masterpiece in schools when it gave their kids nightmares. If you were lucky, indulgent teachers went ahead and read it aloud anyway.
The whole point of these toys was to turn them inside out and watch them "pop." After the third time you set one off in math class, it was likely to be confiscated and never seen again. Luckily, they were easy to replace. Advanced popper owners discovered that it was more entertaining to use suction to covertly stick them to friends' bodies.
While excessive make-up was generally frowned upon in middle school, black lipstick was in a category of its own and had to be washed off immediately. Related item: black nail polish.
Slam books were circulating notebooks containing questions or names of individuals for classmates to respond to. A staple of '80s classroom life, slam books were frowned upon in the '90s for promoting bullying and inappropriate content.
Card game bans ranged from Pokemon to Magic the Gathering. Like Pogs, nerd cards were a seen as a distraction that often led to fights over trading or game play.
Primarily a concern around graduation, Silly String typically was banned to keep the school janitors sane.
Big League Chew
Big League Chew was either banned as part of a general bubble gum ban, or because administrators were concerned that it would promote tobacco use. Related item: candy cigarettes.
Wacky Packages Stickers
These were banned just for the gross-out factor.
Troll Pencil Toppers
Naked dolls mounted atop pencils inevitably led to dirty jokes, but troll toppers were confiscated when more attention was paid to braiding their hair than classwork.
Usually banned by dress code rules for indecent exposure.
These were banned or confiscated due to sanitary concerns. Kids, don't let other kids lick your Ring Pop.
Kool-Aid Hair Dye
Some schools were more lenient about wacky-colored hair than others.
I kind of understand this one. Inevitably, Sticky Hands would get covered in unidentifiable detritus. This made it that much more amusing to fling them at your classmates.
Some schools had an outright ban on ripped jeans. Others only cared about the position of the holes and dealt with students on a case by case basis.