The Latin word for “devour” is devorare or vorare. Of these, devorare is obviously the root of English “devour.” It is formed from the base vorare and the intensifier prefix de-, which indicates a completeness of action, but as vorare already means “to swallow whole, swallow up,” I honestly do not see much difference in meaning between the two.
Devorandum is a form that can mean a number of things depending on context, and without context it does not mean much. (And certainly not “food,” although “that which is to be devoured” is within range – which, by the way, only sounds so weird because English has no comparable form.) For example, you may have heard the famous quote:
Nunc est bibendum.
Now let us drink.
⋯ which was actually written by Horace, a very famous Roman poet, in the late first century BC (Carmen 1,37). (What was Horace so happy about? The death of Cleopatra.) By analogy you can form:
Nunc est devorandum.
Now let us devour.
Unfortunately that does not make much sense even in English. When we say “now let us drink,” we can imagine what we're supposed to drink—alcohol—and apart from that, drinking is a social activity independent of the exact substance we pour down. Not so with devouring, obviously. The exhortation “let us devour” would only prompt confused stares and the question: devour what? and why?
For your game, I would suggest an imperative. That could be:
- Devora or vora (addressed at one person)
- Devorate or vorate (addressed at multiple people)
(There is also a so-called “future imperative,” which is used for laws and general precepts. You may have heard of the boy scout motto Estote parati; in the same vein you could say: Voratote. At that point we're in distinctly weird territory though, in my opinion.)