They usually have photo ops in the hotel lobbies,
HHN merchandise in various shops, and HHN theme at the Red Coconut club in CityWalk. A few minor props may be visible during the day at Studios, anything big will generally be covered up.
Otherwise you need the HHN ticket to do anything related.
Besides the haunted houses, there is also a show or two, walk through themed scare zones, a few rides open, and Deatheaters out in Diagon Alley (and the whole of Diagon Alley is pretty minimal people, so it's actually a nice time to enjoy it and do spells), and themed food booths.
If you don't want to wait in long lines, you could also wait until the morning hours when the waits plummet for most of the haunted houses. Midnight through 2am you can accomplish a lot.
The waits for the haunted houses will vary wildly depending on how popular the house is and when you get in line. Busy houses might have a 2-3hr wait especially before 10-11pm, quiet houses might have a 5-10min wait first thing or after midnight. Pretty sure
Thrill-data.com tracks HHN house wait times if you wanted to take a peek.
Be aware there is a LOT of walking. Although much less if you don't do the houses.
