My neighborhood Wal-Mart grocery had those self-heating coffees on clearance for a dollar each, so I got six. I got the 9.5oz "Hillside Coffee: Double Shot Latte" although they had other flavors. I sent one in my last package to a remote FOB in Afghanistan and asked them to report whether the self-heating part actually works. I'm glad to know they DO work so I'll just send the remaining five in the next five packages.
I wrapped mine in bubble wrap and tape, and packed it in the middle of the box -- but did not put it in a Zip-Loc.The container is metal sheathed in plastic, and it felt pretty sturdy.
I have been buying and sending the "Little Hotties" handwarmers from Costco for three winters now. And I've occasionally used them myself. They're great if you're sitting all afternoon in a freezing cold football stadium. They come in a box with 40 pairs and stay hot for up to eight hours. I forget the exact cost per box, but it was something like $12.
Our Costco also sells bundles with four pairs of Kirkland brand Merino wool hiking socks for about $10. I send one pair of wool socks per package during the winter months, then switch to cotton blend athletic socks for the hot months. This is the best value I have found in winter socks, unless I run into an end-of-season sale somewhere. Warning: Costco quits stocking their wool hiking socks early in the year. So stock up in December or January to have enough for Jan., Feb., March, etc.
Costco also has great deals on Kirkland brand AA and AAA batteries, which I send in every package.