Expect not to get much sleep, or at least have your sleep schedule disrupted. Normal hours are 5 AM to 10 PM, and that's if there's no alliance selection meeting. It gets worse for flying days to/from Worlds.
Hotel eggs are good if hardboiled, egg-flavored water if scrambled. Go with cereal instead. Or waffles if you like them/are a Stranger Things fan.
Competition building interiors are warm, even if outside is not. This is mostly relevant for Duluth.
Speaking from experience here: for the love of god, stay with the group. This is slightly less important at U of M tournaments, where one can catch a bus or the Green Line back to Avalon/GRS (and your parents are probably on pickup duty), but otherwise getting lost in another city is bad.
Don't bring your Switch/laptop/whatever. The stress is not worth it. The mentors will tell you this, I'm just confirming from experience. The one situation to ignore this rule is if you want to bring a laptop to Worlds for schoolwork.
Pick a group you think you can get along with, not people you know. I ended up with my sibling and their friends for Duluth 2022 and got no sleep, along with fighting with my room mates. For Worlds I roomed with Yours Truly™ and another programmer, and things were much calmer and nicer.
Bring more snacks than you think you need.
Regionals are different from Worlds is different from State. The Regionals tend to have lower quality, and are the competition baseline. Teams can show up without much more than a drivetrain, especially in Duluth. Teams have their stuff together by Mariucci, though. Worlds is longer and more intense. There are two ways to get to Worlds: being on the winning alliance at a Regional, or getting one of three specific awards (Impact (historically known as Chairman's), Engineering Inspiration, and Wild Card). Every robot there is a high-quality machine, with scores routinely double or triple that of the average regional. Any gimmick robots (example: the jumping robot at Houston 2022) will be high-quality with all the bugs in the gimmick worked out. State is complicated (see 15).
If possible, acquire at least 3 team t-shirts and a sweatshirt. It makes it easier for the mentors to find you if you are wearing team colors.
When on scouting duty, write the reports as if the team you are scouting would read them. 'Poor Scorer' is fine. 'Sh**ty Vacuum Cleaner' is not. This is partly because we share our scouting data, so there is a chance that they will actually read the reports.
Bring money proportional to the amount of packed lunches you dislike. Competition food is expensive. At Worlds there are food trucks, including ice-cream trucks, so bring money for those if you like ice cream. Or Italian Ice. Italian Ice is good.
Talk with your room mates and make decisions on stuff like sleeping arrangements early.
Keep your phone and room key in different pockets, your phone will wipe the magnet.
Stay hydrated, especially in Houston. In 2022 I didn't drink enough water, and to keep things brief, I went home minus a pair of (boxer) briefs.
The State competition for Minnesota is different than the others. It has no bearing on the main FRC tournaments, and in fact happens after Worlds. The reason it exists is that any Minnesota High School Sport needs a statewide competition. Teams earn points at Regionals based on matches won and awards. It is only a single day, and there are no practice matches before the qualifiers. Scouting happens remotely before the event.
DON'T START FIRES IN YOUR HOTEL ROOM! This actually happened (Duluth 2022).
Take showers and talk to your roommates about shower rules ahead of time. You will likely have to share towels.
There is usually food left over after dinner. Take more if you are still hungry.
If you don't like sharing beds with people, bring a sleeping bag. Pillows make an acceptable matress, and dirty laundry makes an acceptable pillow. If you have enough dirty laundry to make an acceptable matress, something has gone wrong.
Also bring a sleeping bag if you are on a couch. Pullout or otherwise, they don't come with bedding.
Either bring something to soothe your throat or hearing protection, depending on if you want to scream out cheers or plug your ears because the rest of the team is trying to get the Loudest- sorry, I meant the Team Spirit Award.
Addendum to #8: The exact number of teams going to worlds varies depending on the year. Some years the entire winning alliance goes, sometimes only the captain and first pick go. Also, Wild Card awards are generally only ever handed out when one of the teams in a postition to go to Worlds already recived an invite from attending a previous competition.