Very unique question !! Haven't heard anyone raising this !!
I do strategic IT initiatives and teach Intra-preneurship in corporate IT teams.

We have Lull times too - Christmas, Thanksgiving with vacations and low loads.

The best activity to do in this period is "IMPROVE YOUR BOTTOM LINE GROWTH"
1) Improvise process
2) Build systems of functions that are already missing it and not on priority
3) Data Analysis and testing your guts
4) Improve operational efficiency
5) Upgrade resources and systems (includes training)

TOP LINE GROWTH ACTIVITIES
1) Test your hypothesis (related sales and marketing) that are high touch and resource intensive.
2) Build communities around your product and engage your top talents that are otherwise too busy and occupied in your best seasons.

There is a ton of activities you can do...
But everything starts from data. I assume that (because you asked this question), you already own/run a business that is data driven...

Feel free to call me. to have a candid talk.
Don't worry about the $$. Depending on what part of the world you are $$ could convert to a big figure.. Let me know if you need a free pass !! 30 mins .

More than happy to share some of the metrics I use to identify opportunities. Please do share more details about the business if you wish to talk (for a fruitful talk)

Pick a book from your library + read.

Take some time to chill out Than, when you are relaxed and all zen is the perfect moment to think about your business and improve it.

Take a look at your business.

Inventory whatever needs updating.
Imagine expansion opportunities.
Examine opportunities to streamline processes.
Anticipate what you won't have time for during busy season.
Train employees.

Brainstorm options.
Research the costs involved.
Get started.

I determine a period to analyse my performance, make self suggestions for improvements and corrections, and also to experiment with new tools. Then it's on to holidays after writing everything down.

I work on improvements and corrections upon my return, before going back for another cycle with clients.