Primarily horses like to eat grass and hay, and would probably be happy to munch on only this most of the time, but they can be very easily tempted with some sweet treats too...
Polos: (The mints that is, not the game- although they enjoy that too!) It is thought that horses like the mints with a hole because they crave
peppermint oil because it is a natural digestion aid. This has not been proven, though.... And many think that they just like the taste, and it is more likely to be the sugar than the collic fighting properties of peppermint.
Horses also famously love carrots, apples, sugar lumps, and some horses even enjoy the occasionally meaty treat.
Of course, like humans, all horses are different and their tastebuds are developed enough to recognise whether they like or don't like the taste of a piece of food.
Check out these guys eating some watermelon: