Picking out clothes to take is probably the main task but not too many as they won't have the same storage space. We also switched MIL from those old lacy nighties to proper PJ's as she kept flashing her bits.
Nothing that needs careful handling like cashmere as the care home will generally wash on 60 degrees.
We also took MIL's favourite wedding guest outfit so she had something smart to wear when she leaves the care home for the final time, mobid but seemed sensible.
Glasses - will go missing so keep any spares at your house ready to replace when needed. And, for new glasses, get her name shrink wrapped onto them.
Smellies - shampoo, shower gel etc will go missing, don't take a big stash to the care home, just drop off supplies as needed.
Also worth picking out some paintings/ornaments to make the room feel more like home. I can almost guarantee all ornaments will get broken over time though so nothing antique roadshow worthy.
Finally, if you can persuade her to take off rings, its a good idea. As people inevitably lose weight as dementia progresses the rings will fall off and never be seen again.
(Note - where I say missing, I mean missing not stolen. Could be an overworked underpaid carer leaves her bubble bath in the communal bathroom by mistake or another resident wanders into her room and walks off with her glasses etc).