If you have SPD pedals and are only going to ride to the store and back, try asking your LBS about Decksters. I have a pair and they are great. You will need to get a second set of cleats for them as they do not come with cleats. Decksters are aluminum platforms that have a cleat on the bottom and you just snap them into the pedal and ride. They twist off and you are back to full clipless. I use them on both my bikes when I do my Saturday club rides in the city. There is way too much stopping and unclipping and since we aren't going that fast, I don't need the advantage of clipless pedals. I have seen some riders with a homemade version made of plywood and covered with self-adhesive non-skid. Mount the cleats on the bottom and you are ready to go.

Photo's of Decksters on my hybrid.