One really interesting analysis that you can perform is to find out which products your repeat customers are buying.
This is different from just your most popular products.
You want to look only at your repeat customers.
If your store sells a durable good that requires a consumable, like a Keurig coffee maker, it's going to be pretty clear that your repeat customers will be buying more cups.
Knowing which products your repeat customers are buying can help you decide which ones to promote to your buyers list. (You have a buyers list, right?)
It wouldn't make sense to promote the coffee pot to people who already have it, but it would make a lot of sense to promote your 12-pack of cups.
Though this analysis might take time to do, it can really inform your repeat marketing. That's where the money is at.
If you aren't analyzing anything about your repeat customers, this might be a bit difficult to start with.
It would be easier to start looking at your repeat purchase rate because that's the core driver for your entire repeat customer funnel. With Repeat Customer Insights you can get your repeat purchase rate calculated along with dozens of other metrics.
All you have to do is to install it and the automated import will do the rest.