Dumbing this down to just 'beans & rice' is a bit ignorant. In my culture alone we have at least 5 dishes with grain components that all taste vastly different from one another. As to the comparison, grains are often a more 'practical' type of food as they're cheap, have a long shelf life, and are quite diverse, possibly making them more appealing hackers.
Not quite in the same league but a British delicacy has been my hacker fuel for years: Beans on Toast. The name is the recipe, just try and get the proper tins of Heinz beans for true authenticity.
I meant no disrespect here - as I mentioned beans and rice are enjoyed world-wide, in all manner of different styles. I count a few varieties among my favorite food combinations. Thanks for sharing.