Summer Gloves.
Summer cycling gloves not only provide the grip required when riding in the heat, but they also absorb a lot of the vibration transmidded through your bike from the road.
Gloves with padding or gel inserts distribute pressure over a larger area making a long ride easier on your hands. In the event that you do come off the bike, even summer gloves will protect the palms of your hands from most of the inevitable damage that sliding across the road or trail can do.