M.C.
I usually continue with the routine as though she isn't throwing a fit. For my DD, reading before bed is something she truly loves... So it is the very last thing we do before lights out. On nights when she is less than cooperative, I will sit down and start reading without her. She almost always straightens up right away, because she KNOWS I will not go back to a page I already read.... So she will miss her story if she keeps crying.
She also has a set time at night that is the absolute latest she can have a snack. After that, she knows she has to wait until breakfast to eat. She has a small cup of water that stays in her room, so if she cries thirsty I just tell her to get a drink. Whoever starts bedtime (usually me) is the one who finishes it. I never deviate or make allowances unless she is sick, when I might allow her a small snack before bed.
When she gets hysterical (my DD is the same, that when it happens she will make herself sick over it) I hold her, and calmly try to talk to her. I do NOT give in to any of her demands, but I acknowledge whatever it is that is making her so unhappy ("I know you want a snack, but it's time for sleep now. You can have oatmeal with blueberries for breakfast when you wake up though!" Things like that... Just staying calm, acknowledge her feelings, and give her something to look forward to without giving in.) for most regular tantrums, I send my DD to chill in her room until she can calm down... But hysterics (which luckily are very rare...) require a different method for my DD or she will make herself sick... Which doesn't accomplish anyone, and drags everything out while making life miserable for everyone in the house. Lol.