Do get yourself some pesos and buy food from the stalls/windows. It's delicious (freshly made egg tortillas, oyster cocktails, flan pudding hot from the tin), ridiculously cheap and completely safe - food hygiene is fanatically enforced. Also, it's a lovely change from the endlessly repeated chicken/pork/prawns/lobster plus rice plus symbolic amount of salad combo you get in the restaurants. Hard to believe as it is, you can get very tired of lobster.
Is this your business?