These cards were the staples of playground trading sessions and endless games that involved flipping, wall tossing and more. 1. 1971-72 O-Pee-Chee Hockey How can you argue with one of the greatest checklists of all time? This 264-card set features the RCs of Ken Dryden, Guy Lafleur and Marcel Dionne, three players who have to rank among the top-25 players of all-time, along with a solid supporting cast of Richard Martin, Reggie Leach and Rick MacLeish. It also has a brutally tough checklist card (#111) and retirement tributes to Gordie Howe and Jean Beliveau. Plus it delivers one of the…