Serious Eats - seriouseats.com

Classics are always good.

In case you don't know- if you stick a piece of regular sandwich bread in the cookie container, it'll help keep the cookies soft and fresh. The bread gets stale, but the cookies stay soft. My grandmother would send cookies to my cousin when he was stationed in Afghanistan, throw a few slices of bread in the container, and he would always say they were soft and chewy like they'd just been baked the day prior. =)

I would suggest a crisp/dry cookie such as gingersnaps or biscotti. Not a chewy moist cookie that may become hard/fall apart during shipment. I read somewhere that when shipping you should use popcorn to keep things from being getting damaged, rather than packing foam.

Though not technically cookies, I find that brownies always last longer than cookies... and they're sturdier, too. You could even make blondies, which are like a chocolate chip cookie bar anyway. That said, bar cookies are a sturdier alternative to traditional cookie varieties, which could break during shipping.

Perhaps sending a home made cookie or biscotti mix with instructions? I know you said it's a thank you gift, but it would travel really well and they wouldn't get stale. I make a great scone mix that only requires 1/3 cup of heavy cream (mix is 2 c flour, 1/2 c sugar, 1T bp, 1t salt, 1/2 c dried fruit/nuts/chocolate chips, any spices optional. I brush tops with cream and sprinkle with sugar and bake at 425 for 15 minutes)

I mailed standard brownies and chocolate chips to my husband while he was in Iraq. I used Pringle's cans, a round cutter to make the cookies perfectly fit the can, and packaging tape to seal it. I cut 2 rounds of bread for each can, one for the top, and one for the bottom.

For the above referenced cooky order I wrapped each cooky, then made clear cello bags of each type, wrapped the bags in 1 layer of bubble wrap, and shipped. For the cookies that went to Hong Kong, I wrapped each cooky and packed the whole lot in a cardboard shipping box, padded with bubble wrap.

If I were shipping cookies today, I'd stick with bars or squares and wrap them individually. But many years ago, in my early marriage, my husband had to go overseas for a few months for work. After he told me his fellow workers were receiving delicious care packages from home, I baked crisp chocolate cookes and arranged them in a box. I wrapped the box well and shipped the cookies off to my husband. He said when he got them, they were a mass of cookie crumbs! We've since divorced (I don't think it was the cookies; there were other factors). I've learned my lesson (both in baking and relationships).

Thanks everyone!