Surf Rat - You'll get lots of responses but two little unknown gems in your neck of the woods - Banana Beach. Walk out of the hotel and hang a left. Go past Mata Rocks and Caribbean Villas and across the dirt road is a little cinder block place called Emerald II. It's a Chinese place with awesome fried chicken served with Lo Mein, Fried Rice or French Fries - $3.50 US and will easily feed two people.
Go right and down a little, there is Antojitos Santelmo - a screened in place with local type food. My wife and I both ate their one day, breakfast, lunch and dinner and it was $15 US for both of us. Nothing fancy at either place but good basic food for reasonable.
Don't expect stellar service or lots of chit chat as these places really cater to locals and some of the med students. Don't get me wrong, the people are nice but these aren't places you go for great service, you go for good, inexpensive food.
There are also two little grocery stores - one right across from Beach and one across from Antojitos where you can get beer, tortillas, snacks. Be adventurous and forgo the oreos and american snack foods. Try mexican brands of cookies, crackers, etc. Just as good and very inexpensive. Plus you can't beat the fresh tortillas and fresh squeezed OJ sold all over the island. You'll get hooked on those items.