I booked SFO-LAS online coach (I assume that's what they called main cabin).
I understand they charge $25 per bag check in.
Do I need to buy this baggage online first? Or, I pay this at check in time?

What is their regulation on carry on that is free of charge? Brief case? Backpack?

I also assume this 1:30 hr flight is without beverage nor food?

Thank you.