Safe foods (same foods) are basically foods that don’t mess with sensory issues, dietary preferences, etc. They tend to stay the same in texture, taste, smell, or other factors. The person usually keeps them on hand or chooses them at a restaurant without worry that they won’t like it. (It varies from person to person and some do change safe foods for reasons including new preferences and taste profiles, lack of consistent availability, higher costs and a particular experience with the food had caused distress.)
Again varies person to person but commonly discussed as safe foods: rice, bread products (especially crackers), dino chicken nuggets, macaroni and cheese, squeezy apple sauce, easily prepared foods for low spoon/energy days.
These are often comfort foods.
Many also choose safe foods based on dietary preferences related to gastrointestinal difficulties or allergies.
Commonly discussed as not safe foods: fruits and vegetables that vary in squishiness, amount of juice or sweetness or tartness; smelly foods; foods with weird textures. These again can vary and some autistic people may not have the same issues with certain foods that others do. Someone’s safe food can be another’s problem food.