Is there a way to avoid using the public/extrn functions for every sub routine/data/equ/set between two asm files?

This is usually the wrong question to ask if the mass of definitions and declarations becomes too cumbersome.

If that happens, the question that needs to be asked is "Was the code divided into optimal parts ?", and usually the answer is "No.". Code that has lots of variables and functions in common should go into the same file, which minimizes the amount of public declarations. Code that only communicates over a very narrow interface (for example - file A only calls two functions in file B) should go into separate files.

Wildly declaring variables public and modifying them in dozens of different places usually leads to debugging nightmares and should be avoided wherever possible.