At the end of Star Wars: The Force Awakens, when the resistance was finally able to find Luke's location, we can see Rey with a new outfit and she goes to Ach-To to find Luke with wearing it. But how did she manage to get her new clothes?
It's a "flight jacket". Given that the whole base is a staging area for the Rebellion fleet she almost certainly requisitioned it new from the Rebel quartermaster or just picked it up wherever they stash clothing that used to belong to one of the pilots who got themselves dead.
Rey headed to the launch area with R2-D2. Leia waited near the boarding ramp. She adjusted the fit of the new flight jacket Rey wore. “I’m proud of what you’re about to do.”