Question: As the sole product designer in my past two startups I have been an essential piece towards bringing the product to reality (user research, ux, visual design, qa). However, in both situations I found myself not sitting at the leadership table when discussing the future of the product. 

Marketing, sales, support, development all had multiple employees and each department head would get a seat at the table, while I found myself on the outside looking in.

I brought this up several times (along with trying to lobby for more resources in my "departments") in 1-1 meetings with the owners but to no avail. I possibly have delusions of grandeur, but in my view if anyone should be at the table with ownership it would be the individual that is creating the experience that customers are going to pay for. 

Any suggestions for how to improve/approach this situation or book recommendations that might help?

Answer: 
You Can Sit at My Table When You Improve the Things I Care About
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Your owners (like the users you research) have goals, needs, tasks to accomplish, and metrics to improve so they and their business can succeed. If you want a seat at the table you will need to not only understand those goals, needs, and tasks; but help your owners with them.

The best tactic is to tie the owners' business metrics directly to your work:

* Show how your UX work improved Customer Acquisition by X%
* Show how your interaction design changes reduced support costs by $X
* Show how a redesign attracted a specific angel investor

Once you show your owners that you can directly impact their goals for the better, they will be more than happy to "pull up a chair" for you and include you in the product and company's roadmap.

After showing your positive impact on the bottom line and getting acknowledgement from you owners, then you can request investment in more UX resources (people and tools).
A lot of this is determined by the structure and the nature of the company, and it is not always something that you can control unless you are prepared to spend a lot of time and effort into 'educating' the stakeholders.

For example, a company that focuses on sales and is a startup will probably use UX to tick a box for potential investors, rather than being a customer/consumer focused business that wants to make the user experience a point of difference. You can often tell by the C-suite level makeup of the company (e.g. whether they have anyone with a UX background or a Chief Experience Officer).

A traditional company or business often has many levels of hierarchy, and it can take a lot of communication for the type of insights and values generated by good UX research and design to filter up to the top (I have been in this situation many times before). It is important in those situations to work towards establishing UX design as a capability or area of expertise in the business as a first step towards getting a seat at the table (at least compared to the 'flatter' structure of startups).

So I would suggest doing a bit more research into the background of the company, their product, business model and the team that you will be working with initially, rather than going into a project and expect to be able to make wholesale changes when the focus is probably on delivering a product based on a set timeline (I know that it doesn't sound very user-centric or 'Agile' but then again very few businesses truly embrace both philosophies).