You'll need all the usual equipment, such as a lawnmower, spade and gardening fork, but these will all fit easily into a van. You will also have the room to store various shrubs, compost, gravel and any pots that are needed. The van is the place where you can keep all the tools of your trade.
When you have your own van, you can get to any customer whenever they need your gardening services. Just remember that you'll need to enjoy being out in all weather conditions, but you will always be guaranteed work.