What are some tips for helping drive product roadmap as a product marketer if you don't have data or customer anecdotes at your disposal?

I’m going to assume that by data you mean customer research. In general, it’s difficult to drive a roadmap or any type of strategy without insights.

However you don’t always have to do formal research to understand your customers and to make recommendations advocating for their needs. Some areas you can look at are your own data on user behavior and adoption patterns, popular customer support questions and trends, NPS software comments, feedback from your sales team, website interaction, engagement with your content, and finally ad performance so you can get a sense if a particular product/feature is resonating.

It also helps to look at these things in concert so you see patterns that reinforce each other.

It can be tough to get access to data sometimes depending on how your org or team is setup. Maybe you are small and don't have people dedicated to digging into this, maybe team siloes create too much process or your industry is highly regulated. If that is the case I'd encourage you to go out and get the data yourself - can you test competitor products and write up your findings? Can you have some friends or relatives sign up for your tool and gather feedback? Social listening is another great way to get cursory data - tools like Tweetdeck or SproutSocial can be great for seeing trends in your follower base. I'd argue that some data is better than none and these are good alternative ways to get something. 

The above is helpful for the shorter-term, for the longer-term I think it is on the PMM to figure out how to get the data they need to help drive decisions and direction. This may mean building a closer relationship with the person or team who owns this area, or it may mean taking a SQL course and becoming the resident data expert yourself.

There are various inputs into the product roadmap that Product Marketing can provide, beyond data and customer anecdotes. Where Product Marketing can be most valuable is in connecting the dots across the various insights to share a point of view and answer the question 'why this matters'. For instance, you can share competitive trends but take the analysis a step further to share 'why this matters'. 

Additional inputs into the product roadmap: 

• Competitive Analysis: Understanding key competitors, including primary competitors, competitors in verticals, and global competitors to understand where competitive advantages and disadvantages across the marketplace. Incorporate win / loss reporting and interviews into the process as well. 
• Market Trends: Analyze market trends to understand macro themes that will have implications on the product, marketplace, geos, verticals, and customers. This will especially be helpful for longer term planning. 
• Prospects: What got you here, won't get you there. It's vital to understand the broader prospect customer base beyond current customers to identify what wants and needs you aren't solving for, but need to in order to have step change growth. 
• Customer Insights: Triangulate across qualitative, quantitative, and behavioral input to shape point of view, especially since not intentionally customers say one thing and do another. For instance, explore behavioral data to understand engagement and adoption trends. Additional inputs to include NPS, win / loss reporting, case volume, and themes, Sales input, social media listening, research results, customer advisory board insights, etc.

If you dont have data or customer anecdotes, I'm not sure you should be driving roadmap. Influencing roadmap is an earned outcome and not something to just "do" for the sake of checking a box. Think of the roadmap as a business mechanism, and do you have enough to convince stakeholders that the direction of your company should be steered in another direction? For most cases, that is going to be user data, market research, competitive positioning, customer feedback, etc. Without that, I'm not sure I'd be comfortable trying to take on the responsibility of driving roadmap.