I like to warm it up and eat it with milk.
Keep it till Christmas this year and regift it. A lot of the ones I've come across last for years. In my experience, if I was facing an apocalypse and needed to store food, the Christmas pudding is damn near indestructible, and only gets boozier as it ages. If you leave it out in the sun/oven for long enough, they go rock solid (the ones without the booze in them). So maybe you could use it as a doorstop? 10/10 would recommend for doomsday prepping.