How to survive 9 hours of back to back classes?

You should go complain. From what I know, it's illegal for teachers/profs to let their students stay after classes. At least it's illegal from where I'm staying. But if you have no other choice then I guess you could just look on the bright side. This is your future and just think of the reward you get after all the struggle you've faced will finally end.

Part of what an employer knows when you submit a resume with "Degree" checked is that here is a person who had endured some hellish class schedules.researched libraries for information, endured long labs to finish a project. This is the type of person a company wants as an employee. Tough it out and don't cry.

I always bring lots and lots of snacks and put them into plastic bags so that it makes little noise when you're trying to eat it. You've gotta practice how to eat secretly xD if you arent allowed to eat openly. Eat something with protein because it's more energy lasting. Bring lots of water too.

A tiny spray bottle with water to wake yourself up? That's what I do

Interact with the people around you to keep yourself energetic.

I dont really know... i never had such long back to back classes Good luck xD

Please don't let your health deteriorate from not getting time for food breaks. Perhaps you can talk with a student advisor or school counselor about how to have more time in between classes (such as taking a weekend class instead). If you're not in good health from all of that stress and malnourishment, you may not do as well, know what I mean.

Read the bios of famous scientists who stayed in the lab from 5am till midnight 7 days per week. If your motivation is money/med school, then go volunteer at a soup kitchen after labs finish so you can get a taste for what you will be eating daily for the rest of your life if you fail, plus also pick out your future spouse and see if you click with any of your future friends.

Attend first 3 hours then sleep in the class

You can't. It's impossible. You can't even bring snacks because it's against the rules to eat in the lab. This is just typical of the unreasonable expectations society has of people today.

Bring snacks and realize that the alternative is 9 hours of a minimum wage job until you die, be thankful and quit yer b*tchin.

That's tough. Hopefully your professor gives breaks

Eat snacks between classes, you'll be fine