There are many types of bikes that may be used as utility or cargo bikes. This one is an example of the most common bike, the mountain bike. Mountain bikes come with a wide range of gearing although many could use lower gears for our hills. It is relatively easy to go to your local bike shop and have the gearing lowered. A mountain bike allows the rider to sit in a more upright position than the old road bikes, which is usually more comfortable but reduces speed because of increased wind resistance (noticable at higher speed). Bikes are designed for men's longer backs, so women may have to shorten the distance from the seat to the handlebars to be more comfortable. If you have ever been on a road bike and had a sore neck from looking up, chances are that your handlebars are too far from the seat.
Most bikes will need to be outfitted with fenders and racks for carrying goods. Good lights are important if you ride at night. If you don't plan on riding at night, you still should at least have a rear blinky like a Planet Bike Superflash in case it gets dark before you get home. I recommend a flashlight for a headlight for emergencies. You can take it off your handlebars if you get a flat or drop something or want to use it for camping or around the house. I have found Romisen RC-N3 from ShiningBeam.com for $25 to be a great light. I use a Two Fish Block to attach it to the bike. I have bought a dozen of them so I could make them available for $30 for the set (my cost, I am not in business). Contact me to see a few different lights at night. Most bike lights in this price range are too dim for my old eyes. Bicyclists that are frequently riding in the dark should get more lights. Be aware that if you are only using a single light in front and a blinky in the back, cars have a hard time determining where you are on the road. It is hard to gauge distance with a little point of light and the white front light can easily be mistaken for a distant porch light.
Xtracycle
The next move up the cargo ladder is an Xtracycle (brand) or longtail style of bike. This attachment moves the rear wheel about 15 inches back, allowing more room to haul cargo. When I put one of these on my bike, I became aware of the difference it makes to keep the weight between the axles. To explain: The distance between the front axle and the rear axle and anywhere above that line, is where you can carry weight and not seriously effect handling of the bike. If you put much weight outside of that, you will notice the bike becomes a bit less smooth. I really noticed it when touring with large panniers on my bike and the bike felt like it I had a big fishtail. With a longtail style of bike, the heaviest part of the load can remain inside of the axles and it handles like an unloaded bike even with a hundred pounds on it. I carried 200 pounds of mortar mix this summer and it was pushing it when I went up Clay Street out of Kai Tai park to get to Uptown. I haul quite a few tools and even hauled a 6x8 beam that was 12 feet long. A very useful addition and there are a number of them in town.


Big Dummy
There are now a number of longtail bikes coming out that are built that way from the beginning, such as the Big Dummy. Search for Longtail Cargo Bikes and you should find a few.