Since getting back into modeling I've discovered Fun-Tak. It's designed to stick pictures and such to the wall.

it has a unique characteristic of not drying out. I've used a quarter size ball for several years now and it's still going strong. Here are some of the tasks I use it for;

1. Masking camo patterns. The paint will not change its properties after use.

2. Setting toothpicks in little balls of it for holding small parts for airbrushing.

3. Rolling thin rods of it to seal my cheap Chinese airbrush nozzle parts instead of beeswax. You can use a small ball of it to dab the excess away.

4. Plugging holes where you don't want fluids to enter.

5. Make two little mounds of it to hold two small pieces in place for gluing.

6. Holding PE parts in place for adhesive.

7. I've used it to hold hypodermic needles (machine guns) in place before gluing the wings shut.

8. Use your imagination.

1 attached image. Click to enlarge.

You are right, Mike @micrometer, this is cool stuff. There are several versions of this out there, and they are all useful. I even found Silly Putty on Amazon. You don't realize how useful this stuff is until you try it.