@Hugeisno1 items stay unlocked when you cross between worlds through the Seaworthy. The only things you can't craft in SW that are only accessible in a RoG world, like the items under the Ancient tab. Also boss related items like Eyebrella, Hibearnation Vest, Insulated Pack, Scalemail, etc. Luxury Fan seems to be removed since SW already has Tropical Fan, could be a mistake or could be intentional.
There could be other stuff I'm forgetting but with regards to the basic items that can exist both in SW and RoG, unlocked items stay unlocked in both worlds. For example, if you craft the Science Machine in SW (don't place it down by pressing right click) then use the Seaworthy to get to RoG then you'd still be able to place down that Science Machine. Another example, in the RoG World you craft three Boards and unlock the Chest through the Science Machine you just built and cancel the placement again. Then use the Seaworthy again to get to SW, you'd still be able to place down the Chest in your SW world.
I hope that makes sense, cheers.