Hay, water, sometimes pellets. Check for illness.I don't have horses and am trying to remember what a horse would need when being horse sat. Would just be flakes of hay and water right? Make sure no injuries.
Alfalfa is the hay mostly used where I grew up and what any relatives with horses fed them.
I went on a trip back in November. Hired a pet sitter for the first two days and neighborhood kid for the others. Seeing who would do a better job and be reliable in the future. Turns out kid lived on a dairy farm few years back. Pet sitter… let’s just say she tried to put dog food bowls in the chicken coop because scattering grain didn’t make sense. Probably did great with dogs and cats, but outdoor animals were a nope.