Being able to carry stuff on your bicycle by fitting it with baskets on the front and back will make it hugely more useful as it removes the necessity to have to prepare for carrying things before starting off on trips.
Being prepared for contingencies by having a zip-up bag with tools, a pump and wet weather gear ready by the door ready to throw in the basket will help make cycling much more practical.
You can get bunji chord stretch nets with hooks to stretch over your load.
It's also useful to carry plastic bags to cover whatever you're carrying in case of rain.
Be careful when you're riding with a load in either the front or back as it can really affect your stability and steering.
( In New Zealand ) Baskets for the front of your bike may be available in your local bike shop but it may be more difficult to find larger ones for the back.
Some Mobility Scooter distributors ( in New Zealand) may be able to supply baskets which you could attach to a bicycle.
http://www.mobilityscootersnz.co.nz/accessories.html
David Hembrow is making baskets for bicycles in the Netherlands.
http://hembrow.eu/bicycle.html