Define custom code in a custom page template

I created a custom page template with static sidebars and header, not widgetisized.

Now, I wanted to insert a custom code in the template I created, like when I created a post or a page using that template, I can define it.

Here is the other template
http://www.nazcarpine.com/example
so here, I want the coffee to be changed in every post by defining a custom code in the post, lets call sidepic
as depicted in this image

so what code is needed to be inserted in my template to call that image.

another template is for custom header
http://www.nazcarpine.com/example2

which are different from my main template:
http://www.nazcarpine.com/example