Daily walks are an important part of our routine, and being in the city we have to be prepared for anything. I bring a pre-packed bag, filled with the essentials, in case anything unexpected happens on the walk.
This is our "summer bag". It has enough room to hold the dog supplies, as well as anything else we might pick up at a farmers market or around town.
The most important thing I bring is Direct Stop spray. This is a citronella spray; dogs absolutely hate the smell. If an aggressive dog approaches we just have to spray it and it deflects an attack without hurting the dog. I have never had to use it, but I have heard horror stories of encounters people have had with aggressive off-leash or stray dogs. I would rather carry this then have to deal with a potential attack.
We also carry treats for the walk. I use each walk as a training session: the pooches stop at every corner, wait at alleys, walk "in place" close to me, and "wave" at people. I really like using easy cheese because it's easy to treat with.
We also make sure to bring a toy, in case we stop at an outdoor cafe, a collapsible dog bowl for hot weather, and a towel in case of rain.
My winter bag is pared down a bit. I bought an inexpensive gray flannel bag from the Gap which I keep supplied with Direct Stop, Easy Cheese, extra bags, and hand sanitizer--for accidents.