Q. Since the luz bone feeds only from the melave malka seuda is eating mezonos enough?
A. Poskim rule that on the onset, one should wash and eat an egg-full amount of bread (Mishna Berura 300: 1,2). However, since this seuda is not as obligatory as the three meals of Shabbos, in need one can be lenient and consume only mezonos or at least fruits or other food (Mishna Berura ibid.)
Siddur Yaavetz and Eishel Avrohom (Butatch) recommend that even if one is unable to eat this meal, he should at least set the table properly, as this seuda brings the brocho and hatzlocho of Shabbos to the forthcoming week. (See question 1938 above).
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a