Water!
Goats need access to water at all times during the year. During summer however, they get a lot of their water intake from all the fresh greens they are eating, and drink much less then other times of the year.
We use multiple short water tanks, which are usually made from the bottom third of a plastic drum. These are durable, light and short. This makes it so goats of all sizes can get a drink when needed. They may be hard to see at times, but they are usually in an area where the goats can not push them up against the fence and where we think the goats would be most likely to rest during the hot summer day.
We bring water with us in a large tank to top off as needed. Usually the amount of water we set up on the first day is plenty for the week and we end up dumping most of it out when its time to move.