Since a bush plane is defined by how it is used, a wide variety of different aircraft with different configurations have been used over the years as such. However, experience has shown certain traits to be desirable, and so they appear frequently, especially on aircraft specifically designed as bush planes. None of these traits are mandatory - merely they are commonly seen features of bush planes.
The undercarriage is designed to be fitted with floats, skis or wheel/skis to permit operation from water or snow which are primarily for Canadian, Alaskan and Russian use.
High wings ease loading and unloading, particularly from docks, as well as improve downward visibility during flight and increase clearance to reduce the potential for damage during landing or take-off. A high wing is less likely to be damaged during loading or unloading than a low wing.
Conventional or "tail dragger" landing gear--two large main wheels and a small rear wheel reduce both weight and drag, increasing the load the aircraft can carry and its speed and it reduces excessive stresses on the airframe compared to a nosewheel. A failure is also less critical as a broken tailwheel is easily repaired and won't prevent the aircraft from flying, unlike a broken nose wheel.
Very large, low-pressure tundra tires may be fitted to enable the pilot to operate from broken ground. It is not uncommon for a bush pilot to land and take off from unprepared surfaces.
Piston engines rather than turboprops. Piston engines are cheaper to build and maintain and easier to start without the aid of ground facilities (though in extremely remote areas where avgas can be difficult to acquire some bush pilots prefer turboprop engines that can burn kerosene-derived jet fuel).