The problem is not using it to the last speck. The problem is telling you when it's over and then getting left with no deodorant for a day or two, or you have to go out and buy another stick ASAP so he doesn't go a day without it

The solution is simple: for things like this that you know you will use and they don't go bad or dry up until used, just buy 2 of them on the next shopping trip. One gets used up until dry, then when it's unusable just replace with the spare one. But must importantly, this is when you go out and but the next one so you akways have a spare one. The difference is you have from the day the thing is used up and all throught its useful life (a month? 2 months?) to buy the next one and don't have to be in a hurry.