Keep foods warm at a picnic with rock salt. Heat the rock salt (you'll need lots) using your barbecue before you cook your food. Then, when finished, put your hot food in a smaller bowl in a larger bowl of heated rock salt. Should keep your food warm for 1-2 hours. (Full disclaimer: I've never actually tried this as I don't have a salt mine in my basement but it sounds cool. Give it a try and send us a note/picture to let us know if it works.)