How can I take a break without losing all my stuff?

That will be difficult, although you wont lose everything. If you stop playing then the most you can have is a 3 day shield. After this your base will be vulnerable. Enemies can attack you and kill your troops. (any above the hospital limit will die). They can also take any resources that you have in the warehouses. (the values at the top). Any resources in the items menu are safe though. Try to use up any resources listed at the top of the screen before you stop playing.

You can ask friend / alliance members to try to keep you safe by reinforcing you which may help.

After a couple of weeks without logging in at all your base will disappear from the map. Your resource production will stop.

If your game is bound then when you log in again in the future your base will reappear and you will be able to start training troops again and producing resources.