The most common food source is common Norwegian rats up to a “medium” size (100 to 150g range) for adults.
Picky feeders will often take their native prey, African soft fur rats, over common Norwegian rats. Some people choose to feed ASF’s exclusively but this can be an issue because the snake often gets used to taking only ASF’s and they wont always convert to standard rats. This can be problematic if it is sold to someone without access to ASFs. They’re even illegal without a license in Georgia for example.
A 3rd common prey item is mice. They’re often easier to find than ASF’s and picky eaters will often take them over Norwegian rats. This is especially true with hatchlings who have not yet taken their first meal. You’ll find some ball pythons advertised as “mousers” because they will consistently refuse rats and take mice instead.
Hope this helps!