Get double sided pedals.

Nashbar.com sells some called "SoHo" pedals & they put 'em on sale for $30. Flats on one side & clips on the other.

Also, when you buy shoes, make sure you buy mountain biking shoes. That way, you can still walk like a human when you get off the bike without having to change your shoes.

I have double sided pedals & love 'em. If I take my bike on vacation with me to the beach, I can ride it wearing flip flops to go get ice cream. Later than night, I can go blazing up & down the strip on my own with the clips. Best of both worlds.