I have been installing new windows in our home and using a good bit of caulking in the process. Sealing an unused tube of caulking, for use the next day, or even the next week and beyond, has always been a little problem for me, because I hate to waste part of a tube.

During the window installation, I started wrapping the end of the tube with parafilm. Works great and I always have plenty of parafilm laying around! I am not sure how long it will keep the caulking from drying out, but I am sure it will work for a week on two.