If you wish to disable purchases from your shop at any time, browse to the Dashboard / Storefront settings page.

There is a tickbox for Store Closed - tick this when you want purchases to be disabled on your shop and the Store Closed Notice to be displayed:

Add text into the Store Closed Notice text box to specify the dates you're closed for and any other important information. Then click Save Options to save your changes.

This notice will now be displayed on your profile page:

Also instead of being able to add your products to their baskets, customers will see this note in place of this button:

To switch off your holiday status, simply follow the above instructions but untick the Store Closed option.