I'd switch to clip in pedals right away. Shimano SPD pedals and mountain bike or touring shoes are the way to go, so you can walk around off the bike. It's also safety thing is your bike has a serious mechanical problem you can walk home if need be.
Pedals(can be used with clip in shoes on one ride/regular shoes on the other.
Shimano A530 Sport/Touring Road Pedals - Pedals and Cleats
Shoes
Shimano RT82 Road/Touring Shoes - Normal Shipping Ground