For Rey: A pair of black or gray boots, gray leggings rolled to the knee, a white tank top, gray sleeves for your arms (you can easily cut some off of an old shirt), and a long, gray scarf crisscrossed under a brown belt. Put your hair in Rey's multiple bun style to cap things off.
For Finn: A pair of white sneakers, black cargo pants, a black t-shirt, a brown leather jacket, and a cheerful disposition.