Ben:
I had a chance to look at Schulz's article on erythrurus in his Monograph. The subspecies on Palawan is now called philippinus. He has a few photos and sketches that match very nicely with your photo. The food for erythrurus is listed as rodents, birds and lizards with possibly frogs for juveniles.

Best regards
John

>>Hey everyone,
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>>I recently took a trip to the Philippines and saw this snake. The location; Puerto Princesa, Palawan... about 1km into a cave... Sorry about the terrible photo but I was in a boat and all I had to help the camera focus was a flashlight... possible food sources seen on location... brackish fish and bats... any help identifying would be awesome!
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>>Ben