Is it safe to flush expired food down the toilet?
Depends on the type of food.

Just because it will "go down," that doesn't necessarily mean that it's ok to flush it.  Grease is a rather popular example.

Unfortunately I don't know that anyone has compiled a list of all foods that will clog your pipes or otherwise damage your plumbing, but here's a start:


  
  Oil and butter
  Mayonnaise and sour cream
  Cheese
  Sauces and dips
  Salad dressing
  Cake frosting
  Pie dough
  Gravy
  Turkey and chicken pan drippings
  Fat remaining on plates from BBQ’d steak
  


http://www.elocalplumbers.com/blog/clog-prevention-tip-5461

Grains also aren't good, as they will expand as they soak up water.

If you want a safe place to dispose of a little extra food, imo, toss it in a bag and make a trip to a convenience store.  Toss it in the trash, go in and buy a soda.  The food that would've stunk up your trash can is gone, your toilet isn't clogged, the convenience store guy is happy to have your business, and you're drinking a soda.  Life is good.  :sunglasses: