1. The best way to do Chicago for free is to take advantage of Chicago Park District parks. Besides the obvious activities that the parks offer: picnicking, laying out on the grass, playing on the playground, swimming, playing basketball/tennis/frisbee/etc, and riding or running the miles and miles of trails, there's also free movies, dance and music performances, art galleries and installations, the zoo, conservatories, family activities, gardening, the beach....and so much more.
a. If you're a local, I highly recommend downloading the My Chi Parks app. It will tell you events happening by date or location and it helps you track Park Points, another highly recommended feature of the Park District. (Get points for promoting and attending park events, spend points on tickets to Six Flags, sporting events, restaurant gift certificates, etc.)
b. Things that are included in Chicago Park District for a nominal price: Midnight Circus, golfing, rock climbing, day camps, fitness center memberships, sports leagues, wellness and creative classes...and I'm sure there's more. This post could start and end with the Park District.
5. Food can be an adventure all its own. Instead of trying to do dinner along with another activity, Jesus and I like to make eating out the main event. This works when we want to try out a special restaurant, or eat something unique to Chicago. Examples: getting a bag of Garrett's popcorn, then walking up and down State Street while eating; having dinner at Portillo's in River North and getting soft serve at the Rock 'n' Roll McDonald's across the street for dessert; filling up on a variety of Puerto Rican food from several vendors at the otherwise free PR Fest.
6. Exploration is the best way to make your own fun. Yes, visiting the Hancock or Sears/Willis Tower are fun and something to do at some point, but...sometimes walking around at ground level is fun too. I can't number the times Jesus and I have picked a neighborhood and walked. We might go into a store or art gallery from time to time, or stop to marvel at architecture or sculptures, or people-watch as we walk, but it's enough to be out and about in the city we call home