As you likely know, the sun will get you whether or not it is hiding behind the clouds. That is why we highly suggest you wear sun protection. Hats, sunscreen, and sunglasses are very much recommended, and we recommend reapplying sunscreen at least once during the Summit to prevent sun damage.
The weather in Colorado can vary widely in May and we recommend you wear layers. Pack an assortment of clothes and check the weather the beforehand to ensure you can go either to a warm jacket or to a cool short sleeve shirt. Above all, we want you to be comfortable as you walk through the large field where most of our demonstrations and activities will take place.
There are no requirements for shoes, but much of what applied to clothes applies to shoes as well. Work boots are recommended as the field will likely be muddy and you will be near the equipment, but we would like you to come in whatever shoes are comfortable for you. Again, we suggest you consider the variable weather and the sturdiness of your shoes as you plan for the conference.