Include files or similar without building a user control

Question

Hi, I am a newbie
i am working on a SharePoint site, users need to print off pages from the share point site, depending on the link they choose it passes in paremeter through the query string and sizes the page accordingly.  (A2 , A3, A4)
This part works great.
Now I have a chunk of code, this code is re-used in many printpack pages, in classis asp I could use a simple include where I wanted code included and It would also execute in that order.
Is there something similar I can use.
I have include the code in a txt file
I would like to take the function printPackGenerator() and pull it in with a include file or something similar as this bit may need to change in the future
Anyone got any suggestions?
Any help appreciated.
Thanks
Mark