alrighty, i'm not sure if it's ALL but i know they can be
-specific types of fish/bugs/sea shells
-shirts
-pants
-skirts
-dresses
-umbrellas
-hats
-shoes
-socks
-accessories
-perfect fruit (but it'll be a specific type of fruit eg. the premium might be "perfect apple" or "perfect orange"
-normal fruit (same as above, except just "lychee" or "coconut")
-furniture
-ores
-gyroids
-fossils
-cd/music
-carpet
-wallpaper
Any type of clothing
Any type of fish
Any type of bug
Any type of (perfect) fruit
Any type of ore
Any type of shell
Gyroids, Bamboo, CD's, wallpapers, floors, fossils
oh, can bamboo be premium? idk lets pretend it can be
edit: i posted this at the same time as J087 haha i guess it can!!
another edit omg: i think seperate accessories may be premium as well?? like, i think i've seen "glasses" once but idk i might be making that up