As president of one of the two consulting clubs at my school and an MBB summer intern I felt obligated to help with this posting
Ok - first - Absolutely no to the calculator. For additional prep (assuming you cna't practice at school) search online for some MBA schools case book for practice cases. Otherwise practice with people at school (giving cases helped me a ton - It helped me get into the interviewers head)
Ok - My tips for cracking the case interview:
1) First and foremost know the firm's style!!! Ex: McKinsey has very structured cases with multiple parts. They like to see super structured approaches. Accenture uses real cases (interviewer giving a previous project) consistantly. Deloitte like group cases. Bain likes to see you come up with ideas outside the direct scope of the case. BCG likes pressure interviews. Obviosuly this is grossly generalizing.
2) Smile, smile, smile -> be friendly and make appropriate small talk (without derailing the interview)
3) Saying you are stuck is usually not kosher. that being said there are a few methods I use to work through being stuck. a) recap what you've covered so far b) I go through the c-suite in your head and think of any areas I missed - CEO, COO, CFO, CLO, CMO, CTO, CIO, CHO, CCO, CSO. c) ask for a minute to "compile what you've learned so far." d) got through the big stratefy models in your head (4P's, 3c's, Value Chain, Profitability) e) if you are near the end and you have a recommendation ask for help indirectly: ex: "so far we've covered x,y, z and based on this I believe we can come to a strong conclusion. Are there any other areas that client might want me to review prior to meeting the CEO?"
4) Situation Task Action Response technique (STAR) // CAR etc are commone methods though I found them less helpful.
5) be confident in yourself. It is not uncommon for an interviewer to give a little pushback to see if you will cave in on your ideas.
6) The interviewer is there (for the most part) to help you out. They will guide you so pay carefull attention to thier cues. If you keep getting non-helpful information form them move to a different topic, they are hinting that you are going the wrong way.
7) I did use the big frameworks for my interviews (4c's porters etc) but disguised them
8) While real brain teasers are rare now (but I did get one) they have been replaced with market sizing questions