The Farmers Market on Saturdays and The Flea are both free. Food trucks, coffee and even beer and spirits are close by. Both are held inside at Farm Fresh RI on Sims Ave. They're held outside during the warmer months.

https://www.farmfreshri.org/

Check to see if there's an exhibit at Waterfire Arts Center. They're generally free, but accept donations.

https://waterfire.org/about-the-waterfire-arts-center/

The venues are a couple of minutes apart. You can even walk if you like.