The best attire for a job fair is business casual. For men, this consists of a collared shirt and nice slacks; for women, dress slacks or a skirt and a blouse are good choices. Clothing should be clean and pressed, and shoes should be shined.
Job seekers don't need to wear suits to job fairs unless they're interviewing for higher-level professional positions where a suit or more polished look is expected. Clothing should be comfortable and modest, with no garish colors, plunging necklines or short skirts. Even for jobs where jeans and T-shirts are appropriate work wear, business casual is the best choice for making a good initial impression.