There are many tactics and offers to boost campaign rate but I share the top 5 which will definitely work for you, you can try them:
1. The most important I guess is, to send targeted holiday email campaigns using segmentation. You can segment them on their behaviour like (Year-round vs seasonal shopper, Coupon Lovers etc.)
2. Build a smart holiday email campaign schedule.
3. Focus on holiday email content.
4. Point customers to buy now.
5. Show customers a CTA with offer pages.