I think we need to get more fully thought out cultures, Skyrim felt like it dumbed down redguards to just 'arabs' and the imperials to just 'romans without the togas' and that the nordic culture was litteraly just taken from a few viking misconceptions (with the exception of the he-man leather straps, which should probably have some cultural significance given how impractical they are) . The most justice skyrim gave for an interesting culture was for beast races, and those guys were side-lined. It wasn't much better for oblivion, where the cultural blend actualy led to no culture at all. The sad thing about morrowind was that it did nords better than skyrim did.
Skyrim's idea of culture was very heavy handed: TALOS,TALOS,WE'RE HARD PEOPLE, we spell it 'jarl' like the Norwegians do, WE DRINK ALCOHOL,also we made draugr and faught dragons a long time ago, DAMN ELVES, I was sweet on a girl here. That was pretty much it. What we need is;
Seasons. Nah, seriously, Seasons can add a lot to things. From stuff like what time of year is it bad to go swiming because of dreugh, what can be hunted, what kind of farming and resource gathering goes on. Do people avoid blistering summer heat/deadly winter cold and stay inside for good family time? Have spring-time adventures. Decide to not wage war in some months because it's harder to carry over the extreme weather.
Holidays. Maybe they're celebrating a revolutionary figure, the kindness of an aedra/daedra, moon-sugar,or a good harvest.
Competitions and games. From nord wrestling to Altmer magic shows. Redguard sword dances or Khajiit acrobatics. Throwing horseshoes on poles or generic musical competition. The instruments will change with each culture, and artisan competitions are a feature too.
Regional fighting/magic styles. The khajiit might have a dozen different unarmed fighting styles (one might look like tai chi, another might look like silat, the next might look like a muay boran. ) the Redguards have several thousand ways of using a sword, and several thousand styles of sword. The altmer
Small things. Like the way altmer walk, or the way bretons hold their cups. Simple manners. Titles. Speaking in a different language just to alienate foreigners (or for old traditions, but probably to alienate foreigners)
Actual racism. Beyond 'damn elves, damn Impirials' And probably not something stupid like that dunmer in windhelm who thinks you're racist against dunmer despite being dunmer yourself.
Crazy superstision (which might not actualy be superstition, given the magical nature of the world) Puting a dead rat ontop of a door and having someone walk under it might cause fear and bad luck, whilst a woman on a boat during her period might attract vicious sea vampires that are sure to kill the entire crew. eating saltrice in the morning might confer good luck with animals, whilst whispering 'adoring fan' three times to a mirror may indeed summon the demon. It's always interesting so long as it isn't tried and tested.