in order of importance
1 2 elixirs per day, because they are dirt cheap and allow you to run the event more times.
2 1 copy of SSR weapon, because its your main source of damage.
3 1 copy of SSR eidolon, because they come with usefull buffs/debuffs and pretty good stats
4 1 copy of SR weapon with assault skill, ONLY if you dont have alternative and/or maining the element of the event
5 2 premium tickets, because why not?
6 all Soul P that you can get, since that is pretty uch only source of that stuff, aside from ranking up.
7 as many SSR weapons and/or eidolons as you can get for purposes of limit breaking
8 books, since they are much more easy to obtain during raid events, instead of advent events.