CA law says you have to obtain a temporary sales permit if you are selling tangible property that would be subject to a sales tax if sold retail for a period of 30 days or less (which is the situation here). The permit is free; sales tax on the sales is paid back to the state by you. There are also directions to keep records and other paperwork...
http://www.boe.ca.gov/pdf/pub73.pdf This is a pdf with instructions and answers.
If you are going into the dealer's room as a business or making serious money, I'd definitely encourage a permit and sticking to all rules. However, practically speaking, I doubt anyone will patrol us little people in the Fan Market who will profit a whole $47 from homemade bookmarks and xeroxes. The con does not mention it in their rules so I assume it simply does not assume responsibility for our compliance.
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