Oh the dilemma of period food!!
This is a very real dilemma at re- enactments but a detail that is often over looked for smaller less involved events like picnics, for example. And it is most definitely now picnic season :)
This lovely little site has a history of food from oh you know the dawn of time (and I'm not even kidding) and going till current. It has recipes and period menus. It also breaks it down by meal type too , so you can see the difference between a breakfast and a brunch.
Michael and I used the picnic description from 1908 to help us make our food choices for the Lanterman summer whites picnic last weekend. Even though the event had no real era designation we went in teens and so went with a teens-ish meal.