Often new adjusters will ask if it's required to have a truck to be an adjuster. The answer is no, although if you are going to use a car, try to make it at least a mid size.
A truck makes it a little easier to transport everything you'll be bringing with you, but as long as you have a good dependable vehicle you'll be fine.
I know many adjusters that started out with cars; I myself worked the first two years as an adjuster with my car and later bought a truck. Your fold up ladders will usually fit in the trunk, or you can have an external brace to hold the ladder installed similar to those you see that bicycles are attached to.
Some adjusters prefer vans or SUVs, but be smart, wait until you're working and have saved some money...then go and buy the truck or van you want.
When you do buy a truck or van, be practical, unless you're going to be pulling something heavy you don't need a 40 thousand dollar plus monster truck!! Not only are they expensive but they are gas hogs and difficult to park and maneuver around in...especially if your working up north where some of the neighborhoods have extremely narrow streets.