Thanks! My concern with chocolate is that it will melt in transit... have you had experience with this?

Biscotti - any variety. If packed reasonably well, they hold up in shipping and also have a longer 'shelf life' than many cookies/treats, so you don't have to worry about them being fresh when they arrive. (When my son was in college halfway across the country, I experimented with many a cookie and nothing arrived as intact as biscotti.)

Almond toffee, coated in dark chocolate, holds up very well over long distances. If you're going to ship your baked goods overnight or 2-day, then loaves of banana bread, cranberry bread, or pumpkin bread will keep well. If you're going to send things the cheapest route, it'll take about a week and I wouldn't send anything pre-baked. I get around this problem by sending homemade quick bread, cookie, and brownie mixes. All they have to do at the other end is add eggs, oil, and liquid, then bake.