Hey Lazlo,
I am in a fairly similar situation but I am finding that If you follow the Standard and get a hold of the Interpretation Guidelines, it helps a lot!
Essentially make your way through each point and make sure you have everything that they are looking for in relation to what pertains to your company's work.
Have a pre-audit done as well prior to the actual BRC audit as it will give you a better idea of what they will look for and how the process unfolds.
This website is also a veritable treasure trove of information and help since you can traverse the forums and get help for each section via explanations of sections/clauses and examples of documents with how other company's implement the Standard.
Good Luck and Happy Audit Prep!