I work off board on the weekend so my BO can have weekends to go out of town. I
*muck 8 stalls
*feed the outdoor horses their flakes and grain
*turn the stalled horses outside if it's nice (if not, they go in the arena in pairs as their stalls are being cleaned),
*if they're outside, I prepare their evening grain/supplements and put it in their dishes so it's there when they get brought in
*Put their flakes of hay in stalls
*Bring in the horses on Sunday nights
*Prepare the grain/supplements for breakfast the next morning
*Feed the cats and dogs if needed.
Pretty basic stuff.
Grooming might work too. My barn's full of halter horses that are shown frequently when it's warm. I won't be around in the summer, but if the barn shows, they may need someone willing to give baths.