Chicago Travel Site

I will be traveling to Chicago for a trade show (Sunday, Monday, Tuesday in April) and was wondering about the public tranportation there. I hate to rent a car for 3 days not ever having been there before. $12 for a 3 day pass sounds good, but how are the trains buses on travel time, safety, security, cleanliness, etc.? Where should I go on my free (???) time for some great Chicago food at a budget (under $25) price? I will need to pick up a souvenier for my 12 year old son and something nice for my wife and daughter. Any suggestions? Thanks and I look forward to visiting!!!