Normally what I do is this....for walks or bus rides...unless we're doing a whole day away from home excursion I travel as lightly as possible...also my son doesnt tend to need much stuff...sooo..
him in a back carry, a bag-uh, like a canvas grocery bag or whatever kinda bag you like (I hate diaper bags btw) and I only take whats really necessary-maybe 1 diaper (if I feel he'll need changed), keys, wallet, perhaps a sippy cup and like thats it. If I need to take food, just stash in the bag.
I normally dont take toys or anything else as he can play with whats in the bag or whats around in the environment.
I was in DC for 2 weeks a month ago w/ my son on a bit of a vacation and everyday we did that...him in the carrier and 1 bag w/ a diaper change, sippy cup, keys, wallet and my bottle of water.
worked out well.