Real wood and carbon fibre
Carbon fibre should be used much more in the car industry. Each kilo you carry over the years increases the consumption of your car. Each 100 kg overweight adds an extra litre to the litre/100 km car consumption in a city. Saving 50 kg-s would mean 1000 l of petrol in a 200,000 km lifetime. 1000 l is not just expensive; it also means a massive footprint.
In terms of aesthetics, carbon fibre and real wood composite might be a lovely match to this ultralight car. Dark mahogany (in the middle) goes very well with carbon. The one on the top, horse chestnut wood, is our other candidate.