Of the three areas mentioned above, acquiring some practical living skills is probably the least difficult for our children. All children eventually need to learn something about cooking, doing laundry, handling money, and managing transportation, for starters. The best way to teach these skills to a child with special needs is to break any given skill down into small steps and progressively add to them. For example, with laundry, you can start by having your child put his dirty clothes into the hamper, then progress to sorting into colors, then on to loading the washer, transferring to the dryer, folding, etc. Cooking can start with pouring ingredients for very young children, then on to stirring, measuring, reading recipes, etc. Make a list of things you'd like your child to be able to do by the time she is 20, and then break down each skill into its component steps and start involving your child NOW at the level he is competent at. I've even assigned a "stick together like glue" weekend day, where the parent finds some way, however small, for their child to participate in everything they do that day.
A crucial area to focus on is your child's problem-solving abilities. You have to know what to do (or at least who to call) when you lose your keys, when you run out of something you need, when you forget an item you need for class or work, when you forgot to do laundry and the shirt you wanted to wear is stinky, when you need to tackle a big mess in your kitchen! You can work on turning your child into a resourceful problem-solver at a very young age. Rather than rushing to fix a problem, let your child have a try. Intentionally create situations that require resourcefulness so that your child gets practice. Even very young children can figure out how to reach something with a stick or a chair, how to find a shirt if mommy "accidentally" gives her a doll's shirt, how to choose another crayon if the one you want is lost, etc. Model your own problem solving process out loud for your child- when the power goes out, talk about how whether you will find a flashlight or light candles or open windows , and whether you think you should call a neighbor or the power company.
Finally, consider self-awareness. Success in school and in work depends on knowing when you are overwhelmed or confused, and being able to communicate your need for help or for a break. My son gets very upset by fire alarms at school; he copes by letting the teachers know he'd like a warning, and by carrying some foam earplugs in his backpack. Knowing what she needs to function at her best will help your child communicate with others and make it easier to avoid or cope with stressful situations.
Please don't "fall asleep" and wait until your child is 18 to start thinking about independence! Intentionally give your child practice NOW at life skills, problem solving, and encourage his self-awareness on a daily basis.