The Correct Answer is Move to the shade.
While all 3 actions may help, getting out of the mid-day sun is the best choice in this situation. Seeking shade is a key element in preventing skin cancer, especially between 10:00 a.m. and 4:00 p.m., when the sun tends to be the hottest.
The clothes block very little UV radiation because they're made of cotton. This compares to a sunscreen rated SPF 4. Covering up is the right idea, but dark colors, tight weaves, and clothing labeled at least SPF 30 work better. (More and more outdoor clothing has an Ultraviolet Protection Factor or UPF rating.)
Sunscreen should not be used to extend your time in intense sunlight. Sunscreen is an important part of protecting your skin, but it does not provide total protection. To get the most from sunscreen, choose products of SPF 30 or higher that block both UVA and UVB rays, reapply at least every 2 hours, and use at least 1 ounce or a palm full for an adult.