There must be oodles of recipes for 'punch' on the net. As it's going to be a mixture I'd go with whatever takes your fancy and hope the others like it as well.

As one of the purposes of wassailing was to wish for a good crop of apples next year there should be some apples in there, spices, citrus peel perhaps, nutmeg, cloves. I'm guessing now but I think the country people who indulged in this would have used whatever appropriate ingredients were available at this time of year.

Wass hael!