North American Corporate Food Map
And this is just a general map of how small the group of players are now.
I wish this showed all the connections, though, not just food.
For instance, Pizza Hut, KFC, and Taco-Bell used to be owned by PepsiCo until the late 1990s then they were spun off to their own division (Tricorn, then Yum!). But the link remains, since those places serve Pepsi products almost exclusively.
Nestle owns pet food makers Purina, Alpo, Friskies, and about a dozen others.
And so on. But a chart like that would be monstrous.