[Avodah] Brush teeth after seudat shlishit

[Poppers, Michael]

In Avodah V30n104, RnLL noted, "...we wouldn't ordinarily chow down on half a can of Pringles on Shabbat."  Isn't eating such food at any s'udah shlishis, never mind the one this past Shabbos/9Av, accordingly problematic because it displays a lack of kavod for Shabbos, even if there is no issue of hachanah because it's not obvious that one is eating a lot of a particular type of potato product in order to fast better the next 25 hours?  (Perhaps "a lack of kavod for Shabbos" is not an issue, or perhaps eating food on Shabbos that one [how 'bout a ben-melech] would not ordinarily eat on Shabbos is irrelevant?)  TIA for your thoughts. 

All the best from 
-- Michael Poppers via BB pager