I've gotten a decent system down for shopping and rainy days. For the shopping, I have basket on the front of my bike, which takes care of most small amounts o

I've gotten a decent system down for shopping and rainy days. For the shopping, I have basket on the front of my bike, which takes care of most small amounts of groceries. Next I have two pannier bags that fit on the rear luggage rack, and easily attach/detach for carrying around. A large backpack can be added for shorter rides with little discomfort. Beyond that, I do have a bike trailer, but that is only needed for truly large purchases. For the rain, I've found a common rain poncho to work quite well, by draping the front over the handlebars and sitting on the back part, which keeps it in place. Obviously this is not the end-all be-all solution, but it does make those shopping trips in the rain a bit easier and a lot less wet.