Seems like it could have literally been anything. Fruits, vegetables, any meat. How did bacon and eggs end up being what we think of as the typical US breakfast?
Not to discourage further answers but you might like these older answers:
How did the distinction between the 'English' and 'Continental' breakfasts come about? by /u/agentdcf
How did bacon, eggs, sausage, milk and cereal, etc come to be considered "breakfast food" instead of just any-time food? by /u/hiphopothecary
Why are eggs historically a breakfast food in (at least) America?