Winger Campbell-Ryce, 28, has moved back to east London from Bristol City for the rest of the season having had a spell on loan with the O's eight years ago.
Midfielder Reed, 20, has signed a similar deal from Sunderland and both players could be added to the squad to face Tranmere on Saturday.
Manager Russell Slade told the club website: "There was competition for Jamal so we are delighted he has decided to join us.
"Adam had a very successful spell with Brentford last season. He's technically very sound and has a combative side to his game too, so he will be a big asset to us."
Any reproduction, publication or redistribution of this material without the written agreement of 365 Media Group is strictly forbidden.