S.H.
I hope you get lots of responses because I could use some ideas too!
There are the standard zoo, park, feeding ducks & the carousels.
I've found that my almost-3 year old loves to do chores like unloading the dishwasher, sorting laundry, vaccuming, dusting, etc. When we go to the grocery store he's in charge of remembering the things we need (he gets a much smaller list of things to remember) as well as spotting things on the shelves for me.
We also to a lot of baking together. He loves to make sugar cookies because not only does he get to mix the dough, but roll it, cut it out and decorate.
Regardless of the weather, we play baseball in the backyard as well as "barnyard" golf were we just have lots of balls and have fun hitting them with no particular goal in mind. Whenever I have outside work to do, he helps as well - like by raking or pushing the yardcart.
Have you tried various art projects like making hand puppets (lunch bags work well to start with) or necklaces? Something that works wherever you're at is "I Spy" with him getting hotter or colder depending on the direction he's moving.
It's hard this time of the year, but in the summer we're always at the concerts in the park and taking in little league baseball games.