I recognize that there are several albeit similar descriptions of a traditionalist but none would apply to me. Therefore it’s not for me to offer topics that are"important to traditionalists". However as an almost daily reader of most every post in four different forums here over the past few years (yes, I am a CAF junkie :yup

I can offer what I have observed, namely those topics which seem to be the most discomforting to many of the self-identifying “traditionalists” who post here.
the Ordinary Form of the Mass
receiving Communion in the hand
Extraordinary Ministers of Holy Communion
female altar servers
RCIA
reserving the Blessed Sacrament in a tabernacle not on the main altar
use of guitars at Mass
offering the sign of peace
laity using orans position
holding hands during the Our Father
Second Vatican Council
modern church music
modern church architecture
Also, I have observed that many (most?) who are uncomfortable with items on this list are usualy uncomfortable with most if not all of them.
I don’t mean to be judgmental or disparaging to anyone here and again the list is just this one individual’s perception.