The aim is measuring the resistance of different materials on a surface (friction).
1. A toy car
If this is not possible then an empty pot with a form of weight in it would work to enable it to move when placed on a slope.
2. A board
Chopping board/place mat/ other flat and hard surface that is easily lifted.
3. 5 Different materials
Possible ideas: Foil, card, cardboard, paper, table cloth, carpet, bubble wrap, cling film, sandpaper.
4. A ruler or tape measure