Water can be both liquid and solid.

-> Good and correct sentence!~ ^^ 

Every electric devices can't go through the metal detector.

Better say: Electric devices cannot pass through the metal detector.

Kid's toothpastes usually sweet and tasty.

Better say: Children's toothpastes are typically sweet and tasty. 

Every student in this lecture has their laptop.

Better say: Every student in this class has a laptop. 

It'll never leak if you put it in a Ziploc.

**Good and correct sentence!~ ^^ 

I like the pants with deep pockets.

Better say: I like pants with deep pockets. (*Me too!~ It's so functional. ^^ ) 

All passengers must have there own boarding pass.

Better say: All passengers must have their own boarding pass. (You should use pronoun "their". ) 

If you don't like your gift, I can switch with mine.

Better say: If you don't like your gift, I can exchange it for mine.

There is no application more convenient than this application.

**Good and correct sentence!~ ^^ 

He had smoking time for working frequently.

Better say: He smoked frequently while working.

I have to find any lavatory right now.

Better say: I have to find a lavatory right now. 

You can't bring cigarettes in the cabin.

**Good and correct sentence!~ ^^