We don't know too much about the characters yet, but Rey is on the side of the resistance. And Captain Phasma is on the dark side - she's played by the absolutely fantastic Gwendoline Christie (who also plays Brienne of Tarth in The Game of Thrones.)
I think you'd recognise Rey's costume as coming from the Star Wars universe even if you saw it out of context. She wears familar sandy colours and manages to look very cool while being practical.
Rey is played by Daisy Ridley in The Force Awakens.
Of course no Star Wars costume is complete without a weapon! Rey uses a really long staff and this is an important part of dressing up as Rey. Rey's staff has lot's of detail which is very recognisable as coming from the Star Wars universe.
Captain Phasma Costume
Captain Phasma's costume in The Force Awakens is fantastic. Lots of shiny chrome and a cool cape.
There's also a luxury Disney Captain Phasma costume available. And there's a Captain Phasma Voice Changer Half-Helmet which speaks some of Captain Phasma's lines from the Force Awakens and changes the wearers voice so that it's suitable for commanding First Order troops.
Captain Phasma's Weapon
Captain Phasma uses a blaster. A Nerf Episode VII First Order Blaster should do the trick.
Leia Organa Solo
In the second Star Wars Episode VII teaser trailer we get to see (we assume) Luke pass a lightsaber to his sister.
We haven't seen any Episode VII Leia costumes yet. And her costume is very different to earlier costumes that have been available. We'll be on the look out!