Good question! If look closely at the mouths of Predators, you'll notice that although they are frightening, they don't seem well designed for, well, eating food. How does a Predator masticate? Wolf Gnards studied the arrangement and apparent functions of all ten of an adult Predator's teeth and posed two hypotheses: either a Predator grinds food into a fine paste, like baby food, or swallows its food whole, like a snake. I'm inclined to support the Paste Theory:
Like Robocop, the Predators subsist off a "rudimentary paste that sustains their organic systems." The fact that Robocop eats baby food is pretty good evidence that a big, strong killing machine can thrive off the stuff. Baby food is probably also convenient for space travel like astronaut ice cream or Tang, or like military MRE’s (which are a little more like dog food, but I think a Predator might enjoy that more though). I do have a hard time believing that the Predator race has the manufacturing infrastructure and know-how to market and mass produce Brand X Predator baby mush (with the meaty gravy that babies craze). However, this same sentiment could also be suggested for spaceships/space travel. I like to imagine that faster than light travel requires more book reading and less laser shooting. Most likely if they do eat some sort of gruel it is composed of the bones of their fallen prey; any meat grinder would do in that case.