Now that the winter holiday season is over, you'll want to archive and save any marketing that performed well.
This could be email campaigns, graphics, promotion details, social media posts, or really anything else that you found to work really well.
I'd also recommend saving a few screenshot of your store's homepage, product pages, and any other important landing pages. Being able to see how your store looked in the past can really help to remember how parts worked with each other.
Save all that material somewhere safe. Somewhere that gets backed up regularly. Then you can refer back to it next winter or any other time you're going to run a larger promotion.
Reusing that material can save you time and energy over reinventing everything from scratch. Plus you have a track record with that material already so its performance is likely to be better than anything new you create.
Even better if you note down the results for the season too.
Sales figures, AOV, order volume, etc can all help add context around the material for a future reference. I'd recommend writing down all of the Store Analysis metrics from Repeat Customer Insights in there. Or even a full report export as it's easy to get from the app and gives you snapshot of your store's metrics as a whole.