You wouldn't think you would get arrested for trying to cover the 2012 Democratic convention in Charlotte, NC, September 4 or the Republican convention in Tampa, FL, August 27. But such things have happened before, and reporters have available some resources to support their rights.
One is the longstanding convention reporters' hotline run by the Reporters Committee for Freedom of the Press. There will be a 24-hour operation, multiple local phone numbers, and on-call lawyers at both conventions. The national number is 800-336-4243. You will also want to look at RCFP's guidebook, "Police, Protesters, and the Press." 
Of course, you can always access these and other services via the new RCFP FirstAid mobile app  on your smart phone, which is worth having all year round.
- "Reporters Committee Readies Free Hotline for Journalists Covering Republican, Democratic National Conventions,"  Reporters Committee for Freedom of the Press, August 16, 2012.