I feel embarrassed because our car and things are old while everyone else has new ones. What should I do?

Things exist to meet needs, not to keep up appearances, and your dignity does not lie in their brand. A car that is still safe and working has served its purpose; replacing it just out of embarrassment usually adds debt, not happiness. This embarrassment comes from assuming people judge us the way we judge ourselves, when most of them are busy with their own lives. Look after what you have so it lasts longer. If you want to upgrade, do it from savings, not from pressure. Your worth in Allah's sight is measured by taqwa, not wealth. See family finances.