I want to start with small tip for hot days. 

If you ever had a problem like this:

Here is my solution to it:

1. Take a sanitary napkin.

2. Cut it in half.

3. (I think I don't need to explain this picture).

4. Take out the strip. 

5. Stick it in this place.

6. Enjoy your dry armpit.

Have a nice day. :)