Wrap all foods in aluminum foil or plastic before placing in shipping containers when drying during shipping is a problem. Wrap small items, like candy and cookies, individually. Small plastic bags are ideal for this. Select a strong cardboard box to mail the food in. Place a cushion of crumbled newspaper, paper towels, styrofoam pellets or unsalted air-popped popcorn in the box and then add the containers of food. Finish packing with paper. Securely close the box and label it "perishable." Avoid mailing brittle cookies--chewy, soft, drop cookies, bars, or squares will survive best. Bar cookies are a good choice. Most are moist and keep well. Fruit, date or fig bars, brownies and coconut squares are examples. Wrap individually in plastic to preserve each bar's shape and moisture. Other cookies such as butter or sugar cookies (unless they are both thin) and shortbread, biscotti and Spingerle ship well, too. They tend to be fairly sturdy, so you don't have to worry too much about breakage. And since they already have a fairly dry texture, drying out isn't much of an issue. Place two cookies back to back and wrap them loosely as a pair in plastic wrap or cellophane bags. When wrapping chocolate-dipped biscotti, wrap them paired with another chocolate dipped cookie. Have the chocolate side facing one another, with a small piece of waxed paper in between. Then place them in small bags or in plastic wrap. Nestle "the packets" in Styrofoam, real popcorn (air-popped, with no oil)
If you're not sure how well a food will ship, test it. Place the food in a container and shake it a few times. If it holds its shape, it should mail well. Place the food in a draft (made by a fan or wind) to see if the food retains moisture well.
Hard candies, such as peanut brittle and rock-candy, generally ship better than fudge and divinity.