Before sharing your stack with others, you should eliminate any Zombie products. Zombie products are subscription-based products that someone in the organization subscribed to and is no longer using. Zombie products can contribute greatly to bloated technology expenses. Digging up Zombie products can be challenging and may require working with your accounting department to review pages of credit card data.
One place to start is by using BuiltWith (https://builtwith.com), they offer a free tool that will review your site and attempt to identify the tools currently in use. Though not always 100% accurate— since marketers are generally terrible about cleaning up code and tags on their sites when they stop using a product—it’s a great starting point.
Getting rid of all the products that aren’t being used before starting to look at integrating stacks will simplify the integration process when your respective companies come together.