Anyone who's crammed for an exam knows you can only read the flash cards so many times.

Debate day has arrived, and the candidates who spent days studying factoids and polishing zingers are at last putting away the books and clearing their heads. Some are going to Mass. One is attending a state fair. Others are simply resting.

It's all part of their pre-game regimen, before the packed field of Republican presidential candidates face off on two Fox News debate stages Thursday in Cleveland.

"I am going to go to the Rock and Roll Hall of Fame, I'm going to keep my mind free and loose," former Arkansas Gov. Mike Huckabee said.

A lot is riding on the opening debates of the Republican 2016 primary season. With 17 candidates in the mix, the Cleveland showdown could start to winnow the contenders from the also-rans. While Donald Trump dominates the field right now, the prime-time debate also is a chance for the nine candidates flanking him to rise to the fore.

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    To prepare, they have a range of pre-debate routines and rituals.

    Wisconsin Gov. Scott Walker was attending the Wisconsin State Fair opening ceremonies Thursday morning before flying to Cleveland.

    Former Florida Gov. Jeb Bush was going to Mass with his wife. Then, according to a campaign official, his day will be taken up by a workout at the gym and "vigorous emailing."

    Former Pennsylvania Sen. Rick Santorum also went to Mass Thursday morning and is planning some down-time in the afternoon.

    According to a campaign adviser, Texas Sen. Ted Cruz is spending the day with his family and resting. Kentucky Sen. Rand Paul is doing some interviews. New Jersey Gov. Chris Christie is stopping by a state GOP fundraiser, spending time with family and holding a team dinner. Former HP exec Carly Fiorina might play some solitaire on her iPhone during down-time, according to her campaign. Former Virginia Gov. Jim Gilmore is flying in and out of Cleveland Thursday -- it's he and his wife Roxane's wedding anniversary.

    While most candidates by now have already prepared heavily for the debate, some have made a point of going easy on the cramming. They telegraph a message: We got this.

    Retired neurosurgeon Ben Carson, who will be on the 9 p.m., prime-time stage, told Fox News he's not bringing any notes. "All the notes will be in my head."

    Asked if he's nervous, he quipped, "Not at all, it's not brain surgery."

    Trump, who is heading into his first debate, said he was "not really" rehearsing.

    "I think you have to be yourself," Trump said.

    There will be two debates on Thursday. The debates, hosted by Fox News and Facebook in conjunction with the Ohio Republican Party, will be held at the Quicken Loans Arena in Cleveland, Ohio.

    The 9 p.m. ET debate will include the top 10 candidates in an average of recent national polls. They are Trump; Bush; Walker; Huckabee; Carson; Cruz; Florida Sen. Marco Rubio; Paul; Christie; and Ohio Gov. John Kasich.

    The seven who did not make the top 10 are invited to a 5 p.m. ET debate. They are: former Texas Gov. Rick Perry; Santorum; Louisiana Gov. Bobby Jindal; Fiorina; South Carolina Sen. Lindsey Graham; former New York Gov. George Pataki; and Gilmore.

    In a web video on pre-debate "rituals" released by IJReview, Graham said he typically listens to Motown before a debate to "mellow me out." And Carson, underscoring his no-notes approach, said he gathers sheets of paper with advice on them to "light them on fire."

    Cruz, speaking with Fox News, rapped any candidates running toward "the mushy middle" and gave a preview of his approach Thursday.

    "Every time we run as Democrat light, we lose. I'm convinced 2016 is going to be an election very much like 1980 and that we are going to win by following Reagan's dictum of painting in bold colors and not pale pastels," he said.

    While Cruz has been one of the few Republican candidates not tangling publicly with Trump, the senator denied that he and Trump struck any deal to lay off each other. Cruz, though, said other candidates are "frightened" by what Trump is saying.

    "Not only have I refused to [attack him] but I have commended Donald for having the courage to speak out and in particular to shine the light on the problem of illegal immigration," he said.

    Fox News' Lee Ross, Dan Gallo, Brooke Singman, Patrick Ward, Jason Donner, Jenny Buchholz, Jennifer Girdon and Kathleen Foster contributed to this report.