I've used Dairystix for about six months when sailing; you can leave them in the boat for long periods (in my experience they seem to have a shelf life of about six months) both during the season and when laid up, and it means that I no longer have the problem of remembering to take fresh milk, which doesn't last longer than a couple of days, unrefrigerated, in any case. They are fantastic; but it's a pity they are not sold in quantities of less than 200 - that's a lot of cups of tea! - although they can be frozen.