Custom get functions in template

Hello,

I would like to create a custom function to call a template part. Like the get_header(); or get_sidebar(); I need a function like: get_banner or get_form.

The problem I have now is that parts on the page.php page are used on multiple templates like: page.php, single.php, archive.php but are no part of the sidebar. If I can create a single place to change the content of the contact form or banner only once it will save me time and possible mistakes.

Proberly are creating multiple sidebars or creating widgets area’s a option but It would be nice if there are possibility’s to create a get_banner or etc..

Anyone can give me more info on this issue?