The alter Rebbe's brother related that his brother said we shouldn't be makpid when it comes to food related minhagim (apparently there are more important stuff than food). Hence some will say that in lubavitch "it's not a thing", although it's probably more correct to say "it's not an esek", you eat it and go on. Interestingly, on RH we only say a yehi ratzon on the apple although we do eat other RH foods.
Certain foods are not listed in sefer haminhagim, they are just basic Jewish.
Chicken kreplach I believe comes from erev YK when you're not supposed to have red meat, although many poskim say that meat kreplach we're always eaten then as well, and that a bit of meat is not an issue (kabalistically the kreplach should have red meat covered by white dough)