I strapped the little booger to me and used him as resistance training.
No, not in a sling or a front carrier, in a Kelty Wanderer hiking backpack. We had intially bought it for a Blue Ridge hiking trip, but also used it to haul our kiddo across New York City, Chicago, and anywhere else that was not stroller-friendly. And besides, who wants to sit in a stroller and look at people's knees and butts all day? Not me, and surely not someone at the mind-is-a-sponge stage of life. At the rate kids learn at that age, I am motivated to give him something more interesting to look at than the bottom of some lady's purse.
But even when we weren't traveling, I shoved his little legs into that seat, lathered him up in sunscreen, and we took off on an adventure in our own neighborhood each morning. The heavier he got, the better it was for me, because the added weight of a 30-lb baby+backpack was a great workout for not only my heart but my calves and glutes as well. It wasn't exactly 900-calorie-an-hour cardio, but it was better than pushing a stroller and more satisfying for him as well.
Now my kiddo is too big to fit in his backpack, and wants to wear one of his own. But if you're ready to kick it up and have a kid who would appreciate living the high life, give it a shot!