The first Christmas I was selling t-shirts, I was up all night in the lead up to the Christmas markets madly sewing so I had enough stock to sell.
I learned my lesson. Since then, I work on my Christmas over the course of the year. Every time I spend time cutting and sewing, I prepare one or two Christmas t-shirts.
By doing this, I have stock already prepared, ready for the Christmas rush, so I don't spend all night sewing my Christmas t-shirts. Personalised t-shirts are still available, but as much as possible, I try and have the basic designs done ready to add the personalisation.
This saves me a lot of time and stress, and means that I am ready to go when people order. I also play with some new designs during the year in my quieter times so they are also ready to go for the Christmas markets.
My tip: if you make your own stock, spread the making of it through the year.